Getting the gear out reminded me once again that scuba is equipment-intensive. And almost all of it is needed for a dive. Another good reason to keep it all in one place. A complete set of my stuff is in a large travel bag that I bought at CostCo for just this purpose. It's not a scuba bag, but perfect for the task. I hope it'll hold up to the abuse of many more airplane trips. Things are already beginning to fray a bit here and there. That's probably the difference between a $40 bag and one that costs hundreds.

I was also reminded again just how heavy those tanks are as I shlepped one from my garage through the house and into the backyard. Sure, my steel 95s are monsters and Carol forever advocates the use of smaller and handier tanks for regular dives, but there's just a huge difference between the effortless way happy, smiling divers carry their tanks around in movies and commercials, and how heavy the beasts are in real life. Every time I pick one up I think of cave divers with their doubles, or the deep divers who carry and clip on five or more. Maybe sometime in the future materials science has advanced to a point where compressed air containers, if they are necessary at all, will weigh a fraction of what they do today and people will look at today's gear with the same mix of awe, reverence and amusement we peruse a medieval Knight's suit of armor.

I was pleased that I still remembered how to get the gear assembled. No mistakes there. I know, this must seem trivial to seasoned divers but -- alas -- I am not yet one of them. And I swear, one of these days I'll even learn how to put on my fins more or less elegantly. As is, watching me put them on must be comic relief and raise doubts in onlookers' minds as to my suitability to go under.

But go under I did, and it was great to blow bubbles again. Everything worked fine and, as always, my 12-year-old son had fun looking down with his mask and snorkel and playing with my bubbles. He also practiced his underwater photographer's skills with a Casio in an underwater case. I let him breathe through my regulator just below the surface while I used my AIR2 backup. That's when I noticed a minor annoyance: the nylon tie that secures the mouthpiece of the AIR2 stuck out in the wrong position, poking me in the lip. No big deal, but I always get a bad feeling when factory-authorized service on a potentially life-saving piece of equipment is not done quite right. I mean, if the tie is put on wrong, am I totally sure everything else works okay?

After the 35 minute dive (if you can call practicing in a backyard pool a dive) I was reminded that the end of a dive is really not the end of a dive. That comes only after everything has been taken off, rinsed, put somewhere to dry, and then finally stowed away in its proper place.

Now that my son is old enough to take a scuba class himself, I find myself wondering if I think he's ready for it, and whether I'd be scared letting him dive. I know it's a parent thing to worry, and I'll let him decide if he wants to and when he is ready.

I just finished reading "The Dive -- A Story of Love and Obsession" by Pipin Ferreras. It's the story of a Cuban free diver who set record after record together with his wife, Audrey. A fatal accident killed Audrey during a dive to 170 meters (558 feet) and the book recalls Ferreras life and is also a tribute to his wife. Earlier I had read "The Blue Edge" by Carlos Eyles, also a man who pretty much dedicated his life to free diving, albeit for different reasons. But whether it is records, spear fishing, or just being one with the sea, it is hard for me to imagine how it is done.

Scuba and free diving both take place in the water, but beyond that everything seems different. Scuba dives can take an hour or more. Free dives a couple of minutes or maybe three for accomplished free divers. Scuba is slow and measured movement; free diving means darting down and back to the surface. Scuba means dealing with the gas laws so as to avoid embolisms, narcosis, the bends; free diving has none of that as no additional nitrogen is introduced into the body.

Competitive free diving, of course, has its own rules and governing bodies. There are different categories. In "Constant Weight" the diver follows a line to a certain depth and then swims back up, all on his or her own power. In "Variable Weight" the diver uses a weighted sled to go down, then swims back up. In "No Limit," the diver uses a sled to go down, then inflates an airbag at the bottom and holds on to that to get back to the surface. The depths reached are almost unimaginable. How can they do that?

Apparently, in free diving the rules are all different. With no compressed air to counter-balance the enormous water pressure, the lungs and other air cavities inside the body compress enormously. Conventional equalization of the ears and sinus only goes that far; beyond a certain depth the divers do "water equalization, " i.e. they let salt water into the sinus system in a practice that is described as entirely unpleasant. And another phenomenon takes place when a "blood shift" keeps the lungs from collapsing. It's a residual from ancient times perhaps, from our genetic past, but it works (not that I'd ever want to experience it).

The kind of free diving described in "The Dive" requires extensive planning and preparation. Safety divers on scuba are deployed at regular depth intervals, including the bottom. In those extreme record attempts, that means a diver has to wait at almost 600 feet on Trimix. Breathing gas goes very fast at that depth and it's clear that timing is everything. Once the safety divers are down, the free diving attempt must be made exactly on time. And even so, the deeper safety divers won't be back on the surface to partake in the celebrations as there are hours of decompression time.

Wherever there are records and titles, there are politics and competing agencies and bodies, and apparently that's no different in free diving. In his book, Ferreras describes his life and career, and his intense personality that more or less made him an outcast. Already relying on his own certifying agency, after his wife died in her record attempt he came under intense criticism. One of his own crew wrote a book accusing Ferreras of negligence and wrongdoing.

Knowing my tendency to get deeply involved in topics that interest me, I promised myself not to start research on free diving after I finished the book. But in this day and age that's hard to do. Wiki provides an overview, and Audrey Mestre's final dive is right there on YouTube. Yes, the sled's camera recorded how she is trying to inflate the lift bag at a depth of 558 feet, and it won't inflate. You can watch the whole thing.

Running the scubadiverinfo.com site, I get almost every diving-related accident notice via Google news. I don't post them but file them away. It makes no sense to highlight just the danger and the bad things that can happen. Life is dangerous, even one's bathroom where most domestic fatalities occur. I don't see Better Homes & Gardens Magazine report on that very often. It's not necessary.

I first heard of this accident after Carol's certification trip to Ginnie Springs. A cave diver had died the week prior. He had been deep inside the cave system. There had been silting of the system as a result, it was said, and apparently the diver had gone in there by himself with experimental rebreather equipment. I looked it up on Google News and found just three references to it. Compared to the international coverage of the shark-related death during a shark feeding trip, that's a virtual news blackout. In fact, it was just the Gainesville Sun and the local High Springs Heralds that reported at all, or at least that is what Google picked up.

The reports were brief, but what caught my eye was that this was a diver from my native Switzerland. His name was Mark Fyvie, and the paper reported he'd been diving alone, entering the Ginnie Springs underground and underwater caves through the Devil's Eye entry just past noon. When he had not returned by 9pm, another diver by the name of Corey Mearns went looking for him, and Mark Fyvie was found 3,800 feet into the system. The IUCRR (International Underwater Cave Rescue and Recovery) non-profit posted a new thread on the cavediver.net forum entitled "Fatality beyond the Hinkel" in the afternoon of March 11. The report said the diver had used a side mount/no mount rig for passage through a suspected new lead. It was reported that an IUCRR recovery team brought out the body at 9AM on March 11.

I then searched through Tages Anzeiger, the big local newspaper in Zurich, Switzerland but did not find a mention. However, I quickly found Mark Fyvie's website and this is where everything became very emotional. Zurich is my hometown. I grew up there. Zurich Divers, which he started and ran, was Mark Fyvie's diving homebase. His personal site was not in German but in flawless English, which surprised me. I can usually tell translations from German into English, but his English was perfect.

I saw Mark's credentials. He'd been diving since 1993 and a diving instructor since 2000. He had almost a thousand dives to his name. He was a PADI IDC Staff Instructor, an Emergency First Response Instructor Trainer, a DSAT Tec Trimix Instructor, a DSAT Gast Blender Instructor, and an IANTD Technical Cave Instructor. He was also certified as a Closed Circuit Rebreather cave diver, Trimix diver, cave scooter diver, and specially trained on the Mealodon rebreather. So Mark was certainly no noob or amateur. A look at Mark's diving highlights is a trip around the world. He'd been diving and cave diving all over the place, with extensive cave diving, sometimes weeks at a time.

Mark reported on a two week dive trip to the Ginnie Springs area where they'd penetrated 3,800 feet, past the Hinkel restriction. In April of 2007 he did his Megalodon training with a true diving legend, Jill Heinerth of RebreatherPro.com and Jill was highly complimentary of Mark both as a person and as a skillful diver. Mark himself, on his site, was completely aware of the pros and cons of rebreathers. "Some people who dive rebreathers think that once you buy one you must do every single dive with it." Mark wrote, "I don't agree at all. A CCR is a dangerous device that could kill you at any time, why take the risk of using one on a simple dive that could be done more safely with open circuit?"

Another entry from November 2007 describes a full month of cave diving with the Megalodon rebreather in the Americas. This is where he got his CCR Cave and CCR Trimix certifications and also descended down to 272 feet in Eagle's Nest. He was enthusiastic and wrote, "Now I realise what closed-circuit rebreathers are for - it's totally changed the way I can dive caves." He went on to say, "The bad part is finding a dive buddy for this kind of diving. Even in cave country it's tough and I had to do most of the dives alone. ... Now, feeling rather limited by the duration of my CO2 scrubber, I purchased a new radial scrubber, which should easily be able to handle durations of up to ten hours. I can't wait until my next trip in February."

Again I was surprised by the consistently high quality of his English, then found that Mark wasn't Swiss. He'd been born in South Africa, then had lived in New Zealand, Australia, England, Germany and finally Switzerland. He was truly an international citizen, always traveling and exploring new things and places. Switzerland was not going to be his final destination and even after having been away from my native country for over 30 years, I chuckled at Mark's comment that he yearned "for a place where he can shop on Sundays, take a shower after 10pm". It's true. Your neighbors may call the police if you take a shower after 10pm, shops are rarely open, bars close early and at last in my days, you had to register with the police if you moved from one neighborhood to another.

What made me cry was another part of his website. It was about his wedding. He had proposed to his sweetheart and they were going to get married on September 6th of 2008 in Venice. Mark had it all planned out, described every step. He had his whole life ahead of him. It is just so very sad.

At this point I was abundantly clear that this was not just another reckless diver who didn't know what he was doing. This was an extremely accomplished, very smart man who planned meticulously and left nothing to chance. I have done quite a few things in my life, have moved around, seen many different places, have had different careers, but nothing like Mark who was only 36 years old when he died. Looking at his many other interests, I saw that he'd been learning Japanese and wanted to live there someday, was enthusiastic about biodiesel in Australia, Pilates training in Switzerland, all on top of being a certified Cisco engineer.

But there was more. Mark also initiated a discussion forum for English speakers in Switzerland, the englishforum.ch. There was a need for that as Swiss German is as close to a legal secret code as it gets. Mark had commented that while "he was fluent in German, he was completely baffled by Swiss-German and unable to understand even more than a few words." That's because you cannot learn Swiss German. It is only a spoken language. So Mark created a place to help English speakers in the Swiss society. I know the software he used as I use it to run a large forum/community myself. His setup was, of course, completely up-to-date and nicely customized. An "In Memoriam: Mark Fyvie (1972-2008)" was posted on March 13. Within days it had over 300 replies and testimonies to what a great and wonderful person he'd been and how many he had helped. His work had touched people's lives. From all I read about him, I guess he just couldn't help helping others.

Jill Heinerth herself wrote a post and tribute to Mark, her student and friend. She said Mark was a "peer among a very elite group of the world's extremely accomplished and capable technical divers" and that "Mark contributed more to the cave diving community than can ever be measured." In a eulogy on her own website at rebreatherpro.com, Jill wrote "But the reality is that manipulating your own atmosphere for life support is the most dangerous thing you will ever do. Add to that advanced activities like cave diving and exploration and we are on the razor’s edge."

In the end, Mark's time was up, much too soon. In my reading I have often come across divers' frustration when a fatality is simply dismissed as drowning, leaving up to speculation what actually may have happened, and why. Sometimes it's obvious, often it is not. The Megalodon is a rugged, modular and highly regarded electronically-controlled closed circuit rebreather with redundant electronics and a HUD display made by InnerSpace Systems. Mark had indicated he had purchased a radial instead of the standard axial scrubber. The radial scrubber would be able to last as much as ten hours underwater. Inner Space says CisLunar scrubbers also work on the Megalodon and according to an evaluation of the Meg on spiralbound.net, others do as well, though only the CisLunar is mentioned as being radial. Whether or not that made Mark's unit experimental I don't know.

Now one is not supposed to dive solo, though I've read of many wreck divers who feel solo is actually safer under certain conditions where panic can easily result into two fatalities instead of one rescue. As is, my Cavern/Cave Diver Workbook by the National Association for Cave Diving says to "dive with a properly trained and equipped diving partner and maintain diving team continuity throughout the dive." However, that only seems to be a philosophy and not a requirement. As far as safe cave diving goes, "The NACD strongly advocates diving with a partner as the best approach to safe cave diving." Mark had already concluded that finding a suitable buddy for extended time diving was difficult and that he had to do most of his dives alone.

It is equally important to let others know one's dive plan in case something goes wrong. His dive plan was known as he was enthusiastic about his plans and wanted to share with his friends, and at least that aided in the recovery.

The rest is mystery. I'll likely never know what happened, exactly, and it is none of my business. I did not know Mark personally, but his story, so well documented, deeply touched me. May he rest in peace and his loved ones find some sort of solace, nearly impossible though that is.

It's really an amazing thing, those Florida springs. I mean, when it comes to Florida, most people think of sandy beaches, the keys, spring break madness, alligators, swamps, and -- if they are old enough -- perhaps Miami Vice. They'd probably associate Florida with diving, but in the ocean and not inland and certainly not in some of the clearest, freshest water anywhere. But that is what you get in Florida's springs.

How did it all happen in what most people think is just swampland? Well, the northern part of Florida has a vast underground aquifer with several hundred springs. Together they discharge almost ten billion gallons of fresh water a day, with some of the larger ones contributing hundreds of millions of gallons to that total each day. It's all part of a giant storage system. The water originates as rainfall that then penetrates limestone where it is filtered and accumulates in fissures and holes. Combined with carbon dioxide and decaying plant matter, the water becomes mildly acidic and, over many thousands of years, enlarges cracks and holes and creates passages. What it all means is that there is a vast underground system of caverns and caves, many interconnected, in northern Florida and this is the source of all those springs.

The term "springs" is perhaps a bit inadequate because the vast freshwater resources contained in the Floridian limestone system creates all sorts of natural wonders. There are, of course, springs, and they often come right out of the ground. Somehow I associate springs and rivers as something that originates higher up, in the mountains, and then makes its way towards the sea. But Florida's springs come from underground. When you dive, you often see holes at the bottom, with water pushing out of them. Sometimes it's just little boils in the sand. You see them in the clear water, see individual grains of sand twirling around, and feel the flow when you put your hand on them.

But all that water also created grand caverns, nearly endless caves, and also many sinkholes. When we think of sinkholes we generally think of the evening news reporting on a hole in the ground that all of a sudden opened up, collapsing a road or swallowing a home. Those sort of things are usually blamed on human transgressions such as draining or over-using the watertable. However, sinkholes also happen naturally when water slowly eats away at limestone until a ceiling collapses and forms an open entry into the underground spring system.

A good explanation of all this can be found on the "The Journey of Water" webpage of the Florida Department of Environmental Protection.

What does all this mean to divers? It means that Florida has perhaps some of the best diving in the world, and it is in places where you'd never expect it. Instead of sandy beaches, tropical islands, and dive boats, Florida diving seems all shallow rivers and small ponds, some of which covered in duck weed and hard to spot. Once inside, the water is usually crystal clear. That's because it is not stagnant like in a lake, but constantly replaced by the vast volume of water from the underground springs. This phenomenon is exploited by a good number of popular parks and campgrounds located around those springs. People go there to swim and snorkel and just have a good time.

To me, this is what makes Florida's springs so fascinating. There is endless variety. To some people they offer an enjoyable get-away in one of the well-maintained parks with their lush, prehistoric-looking groves and clear, refreshing ponds. Some come to watch the Manatees which like to hang out in the springs. And some dive the caverns and the caves where things can get quite extreme. Manatee Springs state park, for example, both contains a friendly pond and the entrance to a vast underwater caves system that's testing the very limits of courage, skills and endurance in the exploration of many thousands of feet of labyrinthine cave.

During my online explorations I was reminded again of the thin line that separates harmless, enjoyable fun from entry into a deep twilight zone that's as challenging and dangerous as exploring outer space. When Carol and I last dove the Catfish Hotel sink in Manatee Springs state park, I both marveled at the dreamy underwater world that looked like right out of a Pixar movie and shivered knowing that the dark cavern at its bottom was the starting point of Sheck Exley's explorations into the black unknown of endless caves and also where just a few days prior a young man had died when the water had sucked him into the cave.

Ginnie Springs where Carol certified her class likewise has a bright and a dark side. The water in the small spring/pond area is gin-clear, as the location's name implies, but just yards away, underground, lies a massive cave system that has claimed many lives. None other than the great Sheck Exley almost died at Ginnie early in his cave diving career. And, as she later found out, a week before Carol's certification trip, a cave diver had perished deep inside the Ginnie system. Sometimes, a dark side lies just beneath the sunny, friendly surface, and most never even know it's there.

I was reminded yet again of the interesting role Florida's springs play when I found a website dedicated to Florida Springs with almost 50 trip reports and descriptions of springs, rivers and sinkholes in the state's northwest, north and central regions. The site offers an hourlong DVD, entitled "Florida Springs -- The Unexplored Florida" on a good dozen of the more interesting springs. I ordered it and it arrived just a couple of days later. Watching it was an experience. Not only did I see some of the places I had been to myself, but I was reminded again of the secret nature of those treasures. Even the state parks are mostly visited for picnics or swimming and not that many divers know about them.

I also realized once again how diverse the springs are. Some are popular and easily accessible whereas others are virtually unknown or closed off to public access. Some are bright and friendly, others look dark and forbidding. In some you are not allowed to dive at all, in others you pay a fee at the park ranger's office, and some require special permission. According to the DVD, there are even some where you need to check in with the local sheriff and get permission there.

All of this made me want to go back. I'll most likely never dive a cave, will never see what Carol saw, but I may get my cavern certification and poke around some of the better known ones. I cannot wait.

I think of all the excuses I could have for not going diving. I have no dive buddy here. Work doesn't leave me enough time to go diving. Diving trips cost a lot of money. It's cumbersome to get all my dive gear together. There's no place close-by where I can go diving. The small class of people I go certified never stayed in contact. I wasn't ready for a wreck dive in the ocean when my local dive shop invited me to go. I couldn't leave my 11-year-old son on the shore when I was all ready to participate in a salvage operation organized by a local group of divers. And so on, and so on

But those excuses don't really wash. I may not have a regular dive buddy here, but others have overcome this obstacle. I even do the diving website for a local group of divers who regularly invite me to come to their meetings and go on their trips (I never do). My work really isn't a problem. I run a suite of websites and can do most of my work from anywhere as long as I have a computer and internet access. And finding someone to look after my cat really shouldn't keep me from going on a trip. Yes, dive trips can be quite expensive, but it's not that bad. I could afford one or two year. Yes, I don't live by the beach on a tropical island where I can go dive anytime, but Lake Tahoe is closeby and so is the Northern California coast. And if the four people in my dive class didn't respond to my emails, hey, they are not the only people to go dive with. And my gear, well, it's really all neatly packed in my dive bag. It's a lot of stuff, but I do know where it all is, and I keep it all properly maintained.

So it gets back to the same thing: how can I be enthusiastic enough about diving to get certified, do my advanced class, take the Nitrox class, read enough books about diving to -- in theory -- become an expert, do all the research to do this website, and still not go dive on a regular basis?

It's not that I don't want to. I absolutely cherish the memories I have from my few dives. I think of my first night dive and how spooky that was. I think of snorkeling with the Manatees. I think of diving underneath all that duckweed at Catfish Sink to see a magical world and take a picture looking up from the bottom, exactly where the great Sheck Exley once took a picture. I think of testing all those underwater cameras. And I think of locating Rubicon wall in Lake Tahoe and then descend to 110 feet in 48 degree water. I think about the five minutes of fear and uneasiness I always have before I go under (less so in my most recent dives). And I think of the thousands of pages I read about scuba, then summarized in book reports for this website, and how I resolved to experience some of what I read firsthand.

Yet, here I am with my 30 dives. Fact is, I never did actively seek a local dive buddy. Maybe I am the kind of person who needs a kick in the butt to do something. I don't see myself that way, but at least as far as Scuba goes, apparently I am. That bites. I hate it. Sometimes it seems like, for me, diving is like going to a party. I need a major push to go, but once I am there I really enjoy myself and resolve to accept invitations more often.

As is, I have no one to blame but myself for the measly 30 dives in my scuba log.

Well, now there is a real diving Lotus. Rinspeed, a Swiss tuner and builder of exotic concept cars and other futuristic vehicles built the Rinspeed sQuba, a drivable, divable concept car that really works. Based on a Lotus Elise, the electric-powered sQuba is the brainchild of Rinspeed founder Frank M. Rinderknecht, who never forgot that submersible car from the James Bond movie. “For three decades I have tried to imagine how it might be possible to build a car that can fly under water. Now we have made this dream come true,” Rinderknecht said.

How did they do it? First, there had to be some practical thinking. For example, even though the Lotus Elise is a very small car (only about 150 inches long), the enclosed volume of about 70 cubic feet would have required adding 4,400 pounds of weight. The necessary ballast tanks would have made for a large, bulky vehicle that didn't look anything like a sleek sports car. So Rinspeed decided to build the sQuba as an open vehicle with its passengers using built-in scuba gear while underwater. The car floats on water, then sinks when the doors are opened and water enters the car. However, without passengers it surfaces on its own.

What all did Rinspeed do to make this possible? Well, they removed the combustion engine and replaced it with a variety of electrical motors. For operation on land, the main electric motor makes 73 horsepower and 118 foot-pounds of torque at 4500 rpm. Rinspeed estimates the top speed to be "over 75 mph," but given the weight (less than 2,000 pounds) and power it's probaby over 100 mph. Floating in water, the sQuba uses two propellers in the back, powered by an 800 Watt electric motor each, good for a speed of about four knots. Underwater, propulsion is via two electric 5-horsepower Seabob jet drives that breathe through rotating louvers and expell the water through light but twist-resistant Carbon "nano tubes." That gives the sQuba an underwater speed of about two knots. Power is supplied by rechargeable Lithium Ion batteries. Rinspeed states "the sQuba's filling station is the water reservoir,” referring to the electric hydropower the Swiss are experts in. Operating diving depth is around 33 feet.

When going under, the car's occupants use an integrated air supply system with two gas tanks -- one 15 liters, the other 18 liters -- and Scubapro regulators, specifically Scubapro's classic and very reliable air-balanced G250V second stage. The Scubapro gear and the tanks are mounted behind the passengers.

The sQuba is chuck full of interesting technology, and not only for underwater operation. On land, it uses a laser scanner system to essentially drive itself. For underwater operation, Rinspeed and its partners designed a cockpit and instruments that's inspired by the elegant shape and lines of a Manta Ray. Individual instruments seem to float and have dials that are lined up like lenses. The main control cluster is futuristically lighted and sits behind a protective sheet of glass with a fisheye effect. Controls can be operated even with diving gloves.

How real is the Rinspeed sQuba? Real enough for an impressive video of its operation on land, floating and diving. You can see the movie as well as pictures on Rinspeed's website. It works. But it's also a concept and not meant for production at all. For that, it'd need a more powerful motor, and the market for diving cars is likely very small. But none of that matters. Concepts are limited only by the imagination. "For three decades I have tried to imagine how it might be possible to build a car that can fly under water," said Frank Rinderknecht. "Now we have made this dream come true.” Very cool.

What caught my eye this morning was an article entitled "Deep Calculations, Deep Trouble -- Exploring Safety in Dive Computers." This is a topic I am greatly interested in. I love computers in every shape or form and cannot imagine life without them. But dive computers are somehow different, and I don't feel anywhere near as at home with them as I do with any other computer, and that goes for the ones under the hood of cars and such. I trust my dive computer, and like everyone else, I think dive computers undoubtedly revolutionized diving and made it safer and more convenient. But there are dark sides.

The DAN article, written by Rick Layton, reported on the results of a recent Scuba STAR Network safety survey that investigated how scuba divers use their dive computers, what they know about them, and what experiences they've had with them. The survey didn't have a huge sample, just 42 divers, and may or may not be statistically significant. However, the results are pretty much what I expected, and they are alarming.

The survey said that only 10% of the divers actually learned to use their dive computer with an instructor or in a class. The vast majority simply used the manual that came with the computer, if anything at all. A oood half felt that the training materials were lacking and too complicated or disorganized. The survey also showed that divers are unhappy about the almost total lack of dive computer training in formal scuba classes. They suggested at least a review of all the common features, advantages, disadvantages and problems associated with different types of computers.

An appalling 60% of the respondents reported problems with their dive computer. Many felt screens were unreadable. Others reported blank screens, erroneous data, frozen computers, loss of some functionality, battery problems, and so on. Some computer failed to register depth, failed to display desaturation time, reset themselves, stopped displaying remaining air, or had inadequate rapid ascent warnings. As a result, almost 2/3rd of the respondents said they take along dive tables, and almost a third carries a spare computer.

That is certainly no vote of confidence. And I could definitely relate. Although my own dive computer has worked flawlessly for the year and a half that I have had it, I consider it far from perfect. Its user interface is virtually impossible to figure out. So much so that I have essentially given up trying to understand all the many features it has. I gave the manual several serious tries, but it is so poorly written and organized that I simply cannot figure it out and always give up in frustration. Too bad that there is not a large enough market to warrant a separate "Idiot" book for dive computers. That I understand. But why the manufacturer of my dive computer cannot have a tech writer overhaul their atrocious manual is beyond me. I mean, it could save lives.

The same issue of Alert Diver had another article on dive computers. It was entitled "Living with Dive Computers" and written by Dr. Neal W. Pollock. Dr. Pollock, a research physiologist at the Center for Hyperbaric Medicine and Environmental Physiology at the Duke University Medical Center, listed the various advantages of a dive computer, but also the many things it cannot do, or cannot do yet. However, he starts out saying, "You should know not only which buttons to push to make your computer work, but which mathematical model or model derivation it employs for decompression computation."

I agree, of course, that divers should know which buttons to push, and it's really, really sad that I, who consider myself somewhat of a computer expert, do not know which buttons to push to properly use my dive computer. Heck, I can barely see half the tiny little numbers and symbols on its tiny little low-contrast LCD. But now I am even supposed to know which mathematical model it employs for decompression calculations and, presumably, what that means to me?? Though I have a doctoral degree myself, and in a technical discipline, I don't think that expectation is remotely realistic. And if it isn't for someone like me who always wants to know how things work, I think there are others who may struggle with the concept.

But let's say it'd indeed be prudent to a) learn what buttons to push, and b) know the mathematical models that are used in dive computers. What would that mean? I'd say even the former is nearly impossible. Virtually every dive computer is different. I've seen more than one Scuba instructor unable to explain the operation of a student's Dive computer, and those were good instructors. Dive computers do not have a common interface, like Microsoft Windows or the Mac OS, or eve common controls, like computers have a mouse or a touchpad. So instructors may begin spending as much on dive computer basics as they do on dive tables.

Then they may have to get into the difference between table-based computers and model-based computers. Table-based is simple; the computer just uses the dive tables and quickly calculates all you need to know. But most dive computers are model-based, i.e. they make all sorts of assumptions. The oldest and most traditional model uses the Haldane models, named after the Scottish scientist who developed the theories and tables for the British Royal Navy. Haldane tables and concepts still form the basis for most die tables and dive computers, but there are many others as well.

What this means is that a diver would have to know not only about the Haldane theories, but also about statistical models, variable permeability models, reduced gradiant bubble models, slab models, Series models, and EL (exponential/linear) models. Add to that the various proprietary models, hybrids and assorted secret sauces manufacturers use in their computers, and the likelihood that many divers know what mathematical model their dive computer uses and what that entails is essentially nil.

Can we hope for standardization? Probably not. Will there be ongoing research that in conjunction with advancing technology will result in ever more sophisticated dive computers? Definitely.

One thing I am always aware of when I run is air. Early on I determined that I was going to breathe through my nose the first part of the course and until it gets really steep. Then I remove that restriction and gulp in as much as I can. Ever since I took up scuba, I've been looking at breathing differently. I now know more about how our bodies use oxygen, why we have the urge to breathe, and the whole complex mechanism. When I run uphill -- "run" is perhaps an exaggeration; "slowly jog" is more like it -- I breathe so hard that it just doesn't seem possible that my muscles need that much oxygen, yet the urge is there. And I know that should my air be cut off, I'd instantly ... what? Die? Collapse? Pass out? I don't know, but it's hard to imagine not having air. Fortunately, that's just not an issue when you go running.

Underwater it is. No air, you're dead. That's why sharing air with your buddy is one of the first things you learn in Scuba class. Do not panic. Calmly signal your buddy, then assume the position and use the buddy's backup octopus second stage. Or you may have agreed that the buddy will use his or her integrated backup second stage, like the Scubapro AIR2 I have on my Knighthawk BC, and let the buddy use the primary that has a longer hose. If worse comes to worse and there is no secondary, you do buddy breathing where you share a single second stage on the way up. In theory those are good solutions, but I've always wondered what it might look like if you're at 80 feet with low visibility, your buddy has temporarily gone out of sight, and that is when something goes wrong with the air.

Now I know that by and large, scuba gear is extremely reliable. Things are not likely to go wrong, but there really is always something that can go wrong. Stuff can jam, break, rip, get lost, fall off, or you simply run out of air. And when you're down there, that's deadly. I've read a fair bit about cave diving, something that I'll likely never do myself but that fascinates me, and the first rule there is that everything must be redundant. Every system has a backup, and usually even the backup has a backup. That makes sense. Pretty much everything we use in life has a backup if it is really important. The brakes in a car, for example, have multiple backups.

So why does standard scuba equipment not have a backup for air? Everyone except tech and speciality divers just dives with a single tank, and should something go wrong, it's quickly finding the buddy and sharing. To my way of thinking, that's simply not a very good solution. Especially since there are ways to have backup. They are usually called "pony bottles."

Pony bottles are small air tanks with a separate regulator meant to be used in emergencies. Which makes a lot of sense to me. But from what I can tell, few people use them, and there is an amazing amount of controversy over them. Much more than I'd expect over something that seems to so sensible and logical. The primary bone of contention seems to be size.

One company that specializes in backup air is appropriately named "Spare Air." Their standard model has 3 cubic foot of air, a bit bigger than their original bottle that had just 1.7 cubic foot. The company claims that over a hundred thousand of those little mini tanks are in use. The bright yellow spare air bottles are packaged in neat systems that include mounting gear, an integrated regulator that sits on top of the bottle and does not use a hose, and a carry bag. Problem #1 is that they are not inexpensive. They cost around US$300 which is a bunch more than most big 80 cubic foot tanks. Problem #2 is that neither 1.7 nor 3.0 cubic feet of air gets you very far. The company estimates 30 and 57 breaths, based on 1.6 liters per breath. That's on the surface. Which means it's half that at only 33 feet, and a third at 66 feet. If things go bad at 66 feet, ten breaths won't help all that much, and neither does 19. And even that's assuming that you gulp in just the estimated 1.6 liters, and not a lot more as people tend to do when things go bad. Oh, and they are usually filled by connecting them to your main tank. So if you have a low pressure tank like my big old Steel 95s, then you'll get less air in the baby tanks yet as filling them to capacity assumes you start with 3000 psi.

So what about larger bottles? Pony bottles are made by many manufacturers, and they generally come in sizes between six and 40 cubic feet. They cost less, mostly because they don't come with a regulator, so you have to get one. With these pony bottles it's actually possible to bring along a fair-sized backup, enough to bail you out. But now it becomes a question of balancing the amount of backup air with the inconvenience of shlepping along a sizable second tank that needs to be mounted somewhere. A little 3 cubic foot Spare Air clips on just about anywhere on your gear. A 20 or 30 cubic foot tank, that's already another story.

Those firmly opposed to pony bottles say just that: if it's small enough to not be a bother, it's useless because it does not have enough air to be of any practical use. It simply lulls its user into a false sense of security. If it is large enough to have enough air for a serious emergency, then it is also large enough to slow you down, increase the chance of getting entangled, and just generally is a bother to lug around. So either way, they're no good and relying on your buddy makes much more sense.

Does it? I don't know. I've never been in an iffy situation, and I hope I never will. I do know that the thought of having my own backup sounds comforting. The motto of the Spare Air folks is "Because Self-Rescue is the Ultimate Buddy!" and that makes a good deal of sense. I wonder how the majority of divers feel. I rarely see anyone with a pony bottle, so perhaps most do indeed rely on their equipment and their buddies. Fortunately, I know I can rely on mine, always.

I love dive shops as much as book stores and maybe more. Whenever I go to one, I never spend less than an hour or two perusing all the gear, asking a bunch of questions, compare notes and all the fun stuff we do in dive shops. And I almost always end up buying something that I may or may not need, but that I absolutely have to have.

I was early and they were still gearing up for the Grand Opening. So they set up all the food and drink, and a disc jockey prepped his gear. I got a chance to meet the owners, chat a bit and then look around while the place wasn't totally crowded yet. It wasn't a large store, but it was neatly laid out and decorated, had lots of interesting gear, and some of the high tech touches I am a sucker for. A huge flatscreen ran underwater footage in glorious high definition.

So I grabbed a sandwich and a bottle of water and checked out the gear. They are not a Scubapro dealer, unfortunately, and 90% of my gear is Scubapro, but I love to look at and try out new stuff. By now people were trundling in, greeting and hugging each other and soon the place was packed.

That's when I saw it. In a locked glass case.

It was the Oceanic Datamask, a combination of mask and dive computer. My Open Water class instructor, Chuck Odell, had mentioned it to me early on. As a former Navy SEAL he was close to such things and I think he may have mentioned that he'd get one of the first ones. That's because the Datamask began life as a joint development project between Oceanic and the US Navy's Coastal Systems Station. Its original name was the "Combat Diver Display Mask". The idea was to combine mask and computer, have an optical readout right in the field of vision of the diver, thus reducing the need to interrupt operations to look at a wrist-mounted dive computer. One might argue how important that is in the larger scheme of things, but it is certainly high-tech and a fascinating idea.

So they did it, and the civilian result of it is the Oceanic Datamask HUD, with HUD standing for Heads Up Display. It's been available from Oceanic since early 2007 or so, and the company has been demonstrating it at dive shops and scuba get-togethers. I had never seen it in person, but now here it was, in that glass cage.

One of the Fish Eye Scuba sales staff was kind enough to open the case for me and a couple of other interested parties and so we got to check out the Datamask. At first sight it looks like a regular single-lens black rubber/silicone mask, but then you discover that there's more to it. There are some protrusions on the right side, and the lens is asymmetrical, with the right side of the glass area being smaller than the left. That's to make room for the electronics and also the integrated LCD screen. Doesn't that make the mask heavy and bulky? Amazingly not. The mask really feels like any other mask, it has fairly low volume (which I like), and it has excellent fit, with a well designed skirt.

I should mention here that the Datamask is both air-integrated and wireless. It comes with a wireless receiver that screws into the regulator's first stage. If you wear both the Datamask and a conventional wireless dive computer as a backup, the signals won't cross as they operate on different frequencies.

So how does it all work? Well, it's simply a case of the functions of a modern dive computer being built into the mask. If you look straight ahead, you have the same unimpeded field of vision as with any other mask. If you want to see the computer, you look down to the lower right. This is where the LCD screen sits, but you don't really see it as an LCD screen. It feels more like the data is floating ahead of you in space, or rather in the water.

How do you operate it and what can it do? Here, the Datamask's designers came up with an ultra simple method that uses just two buttons, one on top of the mask and one on the side. Each button has two functions: push and release, and push and hold. Those two buttons control all of the functions and display modes of the Datamask. Like all dive computers, after initial setup it'll simply work if you put the mask on and go dive, but if you want to really use its features, there'll be a bit of studying and practicing. And maybe quite a bit. The Datamask (which is Nitrox compatible up to 50%) has a significant number of screens both for setup on the surface and then for diving. It has automatic altitude adjustment, the main battery in the mask lasts about 160 dive hours and the one in the transmitter 1500 hours, it can store 24 dives and comes with a USB interface cable and software for data analysis on a PC. Setup lets you select alarms, units, sampling frequency, lighting, a concervative factor, and tons more.

When you dive with the Datamask, there's a main screen that displays the usual primary data: depth, air pressure, remaining dive time, air time and a tissue loading bar. Push a button and the display goes on to three additional screens with more data. Those then revert to the main screen. There are also screens for safety stops and deco stops.

Now obviously, I have not (yet) been diving with an Oceanic Datamask and so cannot say how it all works in real life. I do know one thing, and that is huge for me. While I have 20/20 vision I do need reading glasses, and that is forever a pain with wrist-mount dive computers. I tried stick-on lenses that either seem to be in the wrong spot (often due to the design of the mask lens) or come off (at times because manufacturers edge writing on the inside of the mask exactly where the stick-ons are supposed to be). No good. I tried masks with magnification windows pointing down, and found that distracting. Amazingly, I can see the HUD display of the Datamask clearly and in perfect focus! That alone would make me want one!

How DOES it work in real life? Well, I searched the web for reviews and found surprisingly little. A couple of people had used it during one of Oceanic's demo tours and written about it. There was one single actual review of the Datamask. It was fairly brief. The reviewer found the mask amazingly easy to use, felt that the LCD display was unexpectedly basic and at times difficult to read, that pushing buttons on the mask was a bit weird at first, that having one's computer inside a mask made it impossible to show it to the dive buddy, and that a backup was a good idea in case the mask comes off. And he wondered how it works with thick gloves on. All in all, he liked it. On various scuba bulletin boards others had issued various sight-unseen opinions: Too expensive. Can't do this, can't do that. I'll wait until they come down in price.

So what's the price? Well, currently US$1,495. That's one expensive mask, of course, but then again, no more expensive than my own UWATEC dive computer and Scubapro Frameless mask combined. So there.

The guys at the dive shop offered me a deal and I came THAT close to whipping out my VISA card right then and there. I really want that mask. I wish Oceanic would let me test one. Hey, after all I have written over a thousand published reviews of electronic gear. But the scuba industry seems stingy with eval units and so I may have to buy the Datamask after all.

The most common explanation is that as we go deeper, the higher partial pressure of nitrogen has some sort of impact on our consciousness. It's conjectured that perhaps at these higher pressures nitrogen dissolves into nerve membranes and thus causes them to function differently, perhaps affecting the way signals travel inside our brain. Some view that as a cool thing. Jacques Cousteau called it "rapture of the deep," which has a nice ring to it and doesn't exactly sound dangerous. Others have mentioned looking forward to some pleasant buzz. But even Cousteau, of course, knew it could be dangerous.

Almost everyone agrees that nitrogen narcosis can lead to unanticipated feelings and thus behaviors, and that is not a good thing when you have a hundred feet of water above you and your well-being and survival depends on logical thinking and remembering what you have learned. But how can you deal with something when you don't know what to expect, when to expect it or what it'll make you do, if anything at all?

I am an avid reader, and for the past year or two it's been mostly dive books. Nitrogen narcosis is mentioned in almost every one of them. In older books, or when quoting older passages, nitrogen narcosis is often likened to having a dry martini (consisting of mostly gin (or sometimes vodka) and a bit of dry vermouth) for every 50 feet of depth. So if you're at 100 feet, that's supposed to be like downing two dry martinis, and 150 feet three of them. That is a lot of booze on an empty stomach, and poured down the hatch. Others use the "martini law" with different rules, like narcosis effect being like one additional martini for every 33 feet, starting when you reach 66 feet. Some writers describe the martini comparison as politically incorrect.

My friend Dave, a former diver who let his skills lapse and hasn't gone diving in many years, remembers his experience with narcosis. He said he was diving off the coast of some nice, sunny, friendly place when suddenly everything seemed to look really cool and colorful and he saw some irresistibly interesting things down deeper. So deeper he went to check it all out. Next thing he knew his dive buddy had grabbed him and brought him back up to the 70 feet or so where his narcosis had set in. So for him it definitely had been "rapture of the deep," even if it wasn't particularly deep.

One area where most experts and accounts appear to agree is that unlike alcohol induced impairment, you can get rid of narcosis simply by ascending. So the assumption is that the impact of nitrogen narcosis is directly proportional to water pressure, or depth. So if you have the experience and presence of mind (or the luck) to be able to recognize and control narcosis, you simply ascend a bit if the impact of narcosis becomes too much. However, there are dissenting opinions. At least a couple of authors stated that, no, the impact of narcosis lingers, just as does the impact of alcohol. Perhaps not for as long, but it definitely won't just vanish if you ascend.

Everyone seems to agree that nitrogen narcosis is hard to pin down as it affects different people in different ways, that it can manifest itself in different ways, and that its onset is unpredictable even within the same individual under similar diving conditions. Not even the depth at which nitrogen narcosis begins to show itself is a given. Some are affected at fairly shallow depths whereas the onset occurs much deeper for others, and some seem almost immune (or at least able to control it effectively).

The symptoms described in literature vary to a great extent. Narcosis may cause pleasant feelings such as exhilaration, happiness, thrill, giddiness, or negative ones like anxiety, depression, or general gloom. As a result, judgment becomes impaired, vision may become impaired, and things can go bad. Most texts state that nitrogen narcosis affects all divers, that its effects are rarely noticeable at depths of less than 60 feet, that serious impairment happens at around 100 feet, and extreme depths of 300 feet or so on air result in narcosis induced halucinations and loss of consciousness (using the various "martini" rules, that'd be six to eight of them; I'd definitely be unconscious!)

Almost every dive book describes examples of narcosis, and, as expected, they vary greatly. In one book, an experienced wreck diver was said to become "addled" and essentially unable to think and function at just 85 feet. In other accounts, deep dives to well over 200 feet on air describe narcosis as just a minor nuisance. Everyone agrees that environmental conditions have a big impact on narcosis. If it is cold and dark, it seems to affect people worse. Then again, it hit my friend Dave at just 70 feet in friendly, optimal conditions.

These days technical divers use special breathing gas mixes to reduce the impact of nitrogen narcosis. For relatively shallow dives Nitrox, the breathing gas with more oxygen and less nitrogen, reduces the risk of narcosis, though it is primarily used to extend bottom time due to less nitrogen being absorbed into the diver's body. Nitrox is unsuitable for deeper dives because then the oxygen becomes the limiting factor as high partial oxygen pressures result in seizures. The answer is Trimix where oxygen, nitrogen and helium are mixed for optimal results (or least potential for damage) at deeper depths. A certain Trimix concoction may contain the proper percentage of oxygen to give the diver enough to sustain life but not so much as to cause seizures; a percentage of nitrogen that will result in enough bottom time for a given depth without the penalty of excessive decompression stops; and the rest in helium, a costly gas that has its own issues, some of them poorly understood and hotly debated.

There are examples of deep divers who used air and simply learned to cope with the impairment, others who switched to Trimix and praised the sudden clarity of thought they had during their deep dives where they'd become used to having to muddle through, and yet others who paid dearly for avoiding the cost of Trimix gasses in favor of plain compressed air.

So how does nitrogen narcosis affect me? Up to recently I simply did not know as my deepest dives had taken me only down to just under 70 feet. My high altitude dives in Lake Tahoe were different. The visibility was good, but several other factors might well have affected the onset of narcosis. I had never gone nearly that deep. The water was cold, down to 48 degrees. And then there was the impact of high altitude diving where equivalent depth is even deeper than actual depth.

So did it affect me? Well, on the first dive I felt a bit uneasy because it had been several months since I'd been diving and because, following my dive buddy Carol, I quickly found myself deeper than I had ever been before. We stopped around 80 feet or so and I felt uneasy. I looked up, knew I had 80 feet of water on top of me, and suddenly felt a slight onset of panic, the kind where you feel not quite right. When that happens on land, you may lay down or drink a glass of water or whatever. At 80 feet that isn't possible, but I knew I did not want to stop and needed to keep moving to keep the uneasy feeling from grabbing a hold of me. So I slowly swam around Carol, and the feeling passed. When she gave me the Ok? sign, I answered back. Ok. And followed her deeper. I had never expected the dive to be so deep and so impressive, but it was. Carol showed me the depth reading on her dive computer every ten feet and stopped to take pictures of it with her underwater camera. I'd taken mine along as well, the Olympus 770SW.

We were now pretty deep and Carol, who was a few feet below me, motioned for me to come down to her. I checked my dive computer and saw 94 feet. She had wanted me to experience 100, but for now 94 felt enough to me. I did not feel compromised or disoriented or buzzed in any way. On the way down to 94 feet I did realize that I had probably flooded the camera. The 770SW has a depth rating of 33 feet without deepwater housing, and I'd taken it down to 67 and Carol to 77. So it was not that I had simply forgotten about the camera; I simply expected it to continue to work. I did not write that off to narcosis, as in I'd completely forgotten that I had the camera with me. I hadn't.

The second Lake Tahoe dive was the Rubicon wall dive. Here we knew we were probably going to go deep, just not how deep. We didn't even know at what depth the wall started. This time we used hoods and gloves so that we'd be less affected by the cold. Despite the unfortunate flooding episode, this time I took two cameras along, both Sealife Reefmasters. We found the wall at 70 to 80 feet. I'd wondered how I'd feel one I came face to face with the wall, where there suddenly would no longer be a bottom. Once I got there, I felt neither elation nor uneasiness, but simply followed Carol over the wall and down. It quickly got much colder, and Carol, who wore only a 4mm wetsuit stopped at 100 feet. I wore my hefty 7mm suit and felt fine. To the best of my recall, I still felt neither anxiety, giddiness or anything else unusual. I just felt good and in awe of everything I saw, as I always do on dives.

I was proud that I had finally reached 100 feet, but all seemed so well that I decided I wanted to push a little farther. So I motioned to Carol that I intended to go down to 110 feet. I didn't use the proper hand signals. Instead, I pointed at my depth reading, then signaled a number as I would on land. I pointed down, then showed five fingers, five fingers again and then one, for 11, or 110 feet. Then I slowly descended, watching my depth gauge. Once I reached 110, I was satisfied (well, very pleased is more like it), and ascended again to 100 feet where Carol hung. By now she was very cold and we began our ascent.

Had I experienced nitrogen narcosis? Was narcosis what made me feel uneasy for a minute or two on the first dive and also flood my camera, and then brave enough to descend another ten feet once I had reached the magic 100 mark on the second? I don't know. I don't think so as I never felt compromised and never did anything that either Carol or I felt was irrational or out of control.

So I don't know. Maybe I am one of the lucky ones who have a fairly high tolerance for nitrogen narcosis. Maybe it just didn't happen on those two first deep dives. Maybe it did happen and I just didn't notice. I don't know. Most likely I'll eventually find out.

I remembered "The Deep" as a pretty decent movie, though I hadn't seen it in 20 years or so. The novel and screenplay were done by Peter Benchley, who also had his hands in any number of creature movies, including Jaws. Peter Yates was the director, also a man with considerably experience. His movie "Bullitt" with Steve McQueen remains an all-time classic. And, of course, the stars of "The Deep" had considerable drawing power: Nick Nolte, Jacqueline Bisset, Louis Gossett Jr., and actor/writer Robert Shaw who had some 50 movies to his name (including Jaws and a couple of James Bonds) and died shortly after "The Deep" was released in 1977.

So this was diving 1977, and that alone was enough to make me want to see "The Deep" again. But there was another reason. Diving legend Stan Waterman had worked on the underwater scenes of the movie, as both a director and a cameraman. I have met Waterman, a diving legend and now in his 80s, personally and enjoyed one of his eminently entertaining and educational lectures.

The movie is about a young couple vacationing and diving in Bermuda. They dive a WW II wreck and come across a large stash of morphine ampulles, worth a fortune on the drug market. Word gets around, and the bad guys, led by Louis Gossett Jr. are soon on their trail. But there's more. Seems that storms sort of mashed that WW II warship and a much older vessel together, and so there is treasure. Treasure is good, but it's really worth a whole lot more if its authenticity can be established, and so the stage is set. Bad guys after drugs. Good guys doing research on the suspected treasure. Throw in some ghastly VooDoo, motorcycle chase scenes to liven up the somewhat twisted plot, and then there's the diving, lots of it. That's what primarily interested me.

This is 1977, really not that much past all the Cousteau documentaries I'd watched. Yet, whereas Cousteau's footage always had sort of a Buck Rogers back-to-the-future look to it, what with their sleek, futuristic, aerodynamic gear and their double hose regulators, diving in "The Deep" looks surprisingly modern. It must be warm as Nolte and Bisset only wear bathing suits. In Bisset's case, a rather revealing skin-tight T-shirt with prominent nippleage was probably sensuous enough to send censor types into shock. Other than that, modern-looking regulators, modern looking masks, single tanks, nothing that would look out of the ordinary today. Except for one thing: no BCs. In 1977, buoyancy compensators did exist. Scubapro developed the stabilizer jacket in 1971, and so called adjustable buoyancy life jackets had been around since 1961. So I don't know if by 1977, it still wasn't common to use BCs.

The dive masks they used looked like something you'd buy today. Light and clear and low volume. The underwater photography was terrific in every respect. As is usually the case in movies, some things made me wonder. Like, they penetrate this wreck they do not know without protective gear or lines at all. More interestingly, silting never seems an issue. They swim around, push, pull, fight, yet hardly any silting at all. Visibility is always a-okay. The shipwreck used in the movie was supposedly that of the RMS Rhone that sank in 1867, with filming taking place at 75 feet in the bow section. Much of the diving actually looks much shallower than that, which makes me wonder how the picked the title "The Deep." Oh, and this was before dive computers. Still, no one ever runs out of air, and I don't think I saw a single decompression stop or anything like that.

There was some excellent shark footage. The bad guys threw fish and bait into the sea to attract sharks, and the resulting footage is awesome, especially for the time. I could just picture Stan Waterman, that pioneering shark cinematographer, behind the camera, not quite knowing what to expect. Another bad guy critter is a truly giant moray eel in the wreck. Morays always look evil. This one actually ends up crunching Lou Gossett Jr.'s head and biting it off. Ouch.

All in all, it was nice watching "The Deep" again. It is not a very good movie, especially given its illustrious cast, but the dives scenes were great. And Jacqueline Bisset sure looked good underwater. Maybe that's why they didn't wear bulky BCs.

What gives? Aren't all those dive tables based on the same principles? Should they not yield approximately the same results? True, the PADI and NAUI tables are different, with PADI breaking things down into 26 "Pressure Groups" while NAUI has less granularity with just 12 "End-of-Dive Letter Groups." So you'd expect the tables to occasionally produce slightly different results, but not by much. Sometimes PADI would show more bottom time and sometimes NAUI. But that does not appear to be the case. The NAUI tables seem to consistently yield more residual nitrogen time and less maximum dive time for repetitive dives.

Does that mean NAUI is more conservative? I don't know the answer just yet. Based on my own experience, I've come to view PADI as more tourist and recreation oriented, and NAUI as more technical and detailed. If that were indeed so, then one would expect PADI to be more conservative so that its broader and perhaps less experienced diver base stays within safe limits at all times. Instead, the respective dive tables almost always allow less repetitive dive bottom time to the assumedly more experienced average NAUI diver.

Could definitions have something to do with it? Just like the PADI and NAUI dive tables are different, so are the two competing certification entities' terminologies and definitions. As a result, as if dive tables weren't confusing enough, those trained by different agencies must also figure out if "Actual Bottom Time" is the same as "Adjusted Maximum Dive TIme," and "Total Bottom Time" the same as "Total Nitrogen Time." That's just not good.

Looking at my notes and instruction materials, I find that NAUI defines "actual dive time" as "the time from the moment of descent until returning to the surface." Breaking the surface or starting to return to the surface? For PADI, on the other hand, "bottom time" is "the total time in minutes from the beginning of descent until the beginning of final ascent to the surface." So the NAUI "total nitrogen time" which adds "actual dive time" and "residual nitrogen time" would yield a larger number than PADI's "total bottom time" that adds "actual bottom time" (which does not include the time it takes to ascend) and "residual nitrogen time." Confusing for sure.

And there's another difference. PADI states that "if you don't plan to dive for at least six hours, the residual nitrogen has little consequence. True enough, if you look at the PADI Recreational Dive Planner, you find that after a six hour surface interval you are no longer in any pressure group at all and a second dive, even if the same day, would apparently not be treated as a repetitive dive. NAUI, on the other hand, categorically states that "any dive made less than 24 hours after a previous dive" is a repetitive dive. Which means that no matter how long the surface interval on any given day, for the second dive you'll always start out at least in End-of-Dive Letter Group A.

What does it all mean? Nothing for most divers because very few will ever agonize whether to use the PADI or the NAUI dive tables. And most divers simply rely on their dive computers anyway. But those large discrepancies between the tables are still amazing after being taught in class that even a couple of minutes of extra bottom time can be the difference between a safe dive and the prospect of getting bent.

How would diving come in handy for that? Well, with cameras it is obvious. There are many of them that you can take underwater. Most with housings, and now more and more that don't even need one as long as you don't go deep. So knowing camera technology and being a diver lets me take my reviews underwater, and that opened a whole new area for me, one that I greatly enjoy.

But computers? I am not talking dive computers here, the ones we take down to great depths, but just regular computers. So what's this all about? Well, manufacturers realize that not all PDAs and notebook computers will lead a sheltered life sitting on desktops and meeting room tables. Some are used outdoors, some are dropped, some are rained on, and some may even get banged around or crushed. The military, for example, needs the equivalent of a HumVee in a computer, and not some plasticky thing. Anyone who uses a computer as a tool for a job needs just that, a tool, and not a gleaming conversation piece with a panorama screen so that DVDs can be watched on it.

Which means that there is a significant industry out there that makes nothing but tough, rugged computers for special purposes. Panasonic for example, they are a household name with their TVs and electronics, but they also make the "Toughbook" line of notebooks that can take much more punishment than a standard laptop. Companies like UPS or FedEx buy hundreds of thousands of handheld computers they use on the job, to scan and track packages and capture signatures. Those handhelds must be pretty tough to survive all that, day after day and month after month.

There are some standards the industry uses to describe how rugged a computer is. Most come from the military and simply describe testing procedures. The MIL-STD (military standard) alone consists of hundreds of pages of how it's all done. Most countries have their own, and then there are some industry associations and institutes that also have standards, so it can get a bit confusing. Reading and deciphering those ruggedness specifications, and then figuring out what it means in real life, is part of my job. The one standard I think matters more than most is the IP rating. That stands for "Ingress Protection" and was defined by the International Electrotechnical Commission. A mobile computer's IP Rating is expressed as a two-digit number, like IP-56. The first number designates protection from solids (from 0 to 6), while the second number designates protection from liquids (from 0 to 8).

All dive computers would have an IP68 rating if they were tested for that. IP68 means they are completely protected from dust getting inside, and, of course, they are completely waterproof and protected from the effects of immersion. Regular computers are not. They don't have to be. But maybe they should, at least to a degree.

To make a long story shorter, there are some handheld computers with an IP67 rating, which means they can actually be immersed into water and survive. It's just baby steps for now, with immersion usually limited to about a meter and for no longer than 30 minutes or so. And even that is extremely rare. It so happens that I got one of those computers to review and test, a very tough handheld from a company called Tripod Data Systems. Their new Nomad computer is for the military, for surveyors, and others that need to computer and communicate in extreme conditions. It's a very sophisticated unit with a fast processor and a razor-sharp display that puts the Apple iPhone to shame. And it's rated IP67, with 30 minute immersion to a meter of water.

Needless to say, I had to check that out for myself. My regulator and BC had just come back from their first annual service and I was absolutely dying to get back underwater. If I had a dive buddy, I'd have gone up to Lake Tahoe to catch another dive or two before the water gets too cold up there. But I could not find one, and so it had to be my pool.

Preparing for the dive with the Trimble Nomad computer required some planning. First was the mental step in deciding to actually do it -- take an expensive piece of equipment underwater, one that I needed to send back to the manufacturer. What if it flooded? The second was to record the event, and for that I needed cameras. I decided to use a Casio Exilim EX-Z77, also here for review, for the above-water scenes as it includes a cool new "YouTube mode" which means it spits out video optimized for the YouTube video sharing service. For underwater I picked a SeaLife DC600, mounted on a regular tripod. My eleven-year-old son Morgan was my assistant and he certainly earned his pay (in chocolate-covered peanut pretzels).

So I am finally all geared up and wearing my new "Edge" 3-mil wetsuit. I do some preliminary tests by carefully immersing the computer into the water and watch for bubbles. On camera. No bubbles. Now Morgan joins me in the water with his snorkel gear. He holds the only slightly negatively buoyant tripod with the SeaLife camera on it steady and starts recording. I am going down, making sure not to descend deeper than three or four feet, holding the Nomad computer in my hand. I circle the pool, then stop in front of the camera and operate the computer with its stylus. The touch screen operates just fine. I bring up some menus, click here and there - no problem at all. The Nomad, like many handheld computers, has handwriting recognition, and so we try to capture that in a closeup. It works, but the screen is too reflective to get a good shot with the camera, and so that didn't quite pan out. I do a final underwater lap around the pool and surface, with Morgan capturing that on the Casio.

So that was diving with a handheld computer that was probably never meant to be used in scuba gear. But it could handle it, and now I wonder if perhaps we won't be seeing underwater computers sometime soon. They'd sure beat a white slate and a pencil. Perhaps. There are times when throwing expensive technology at a simple problem makes no sense, but I'd like to see it anyway. Imagine drawing, reading an eBook, emailing or testing, or even browsing the web during a long, boring deco stop. Or using the dive slate's built-in digital camera. The opportunities are endless.

As is, I got to dive again, and I got to do something new and exciting. I needed that. An event that I had looked forward to all year was recently cancelled. It was to be my first dive trip to a "real" exotic dive location. I had practically lived for that all this year, thought about it while falling asleep and dreamed how great it'd be, but due to circumstances beyond my control, it won't happen. So that totally threw me for a loop and left profound sadness that I have been unable to shake. I think diving and all that it means and includes is more than just a sport. I am not quite sure what it is, but I know it changed my life.

It's interesting how those courses are conducted. You actually do all the studying beforehand with the coursebook in the crew pack. You also watch the DVD that covers the exact same material, but makes it all look nice and friendly. And you practice with the included dive tables. For the Nitrox class that's plastic dive tables for Nitrox with 32 and 36% of oxygen, and a table that shows equivalent air depth for mixtures with 30 to 40 percent oxygen. On the other side of that one is an Oxygen Partial Pressure table you use to calculate total allowable oxygen exposure for a day.

The course book is organized like the larger book for the initial PADI Open Water class. You read, you underline and you answer questions at the end of each chapter. The idea is not necessarily to memorize every word, but to grasp concepts and know where to look things up. The answers are always given, on the same page, in small print. At the end of each major section is a "knowledge review" that you fill out and sign. No answers given there. Studying and understanding all the materials takes some time, and then doing all the dive table examples takes some more. It's not necessarily very difficult, but it is important stuff that people from all walks of life need to understand before they go diving with Nitrox. Bottom line: you need to set aside several hours of concentrated worktime to prepare for the class.

The class itself was full. 12 people at least in a small but neat and well organized and equipped classroom. Our instructor was Rick Rowett, a PADI course director, which is as high as it gets in the PADI hierarchy, and also the manager of the Dolphin scuba store. And, as he later told us, a reverend. Rick was personable, knowledgeable and did a great job. The class essentially consisted of going through all questions of both Knowledge Review sections, with detailed explanations if someone had gotten it wrong or did not understand. A good approach, assuming everyone had indeed done their studies beforehand. Rick threw in a lot of explanations, advice, and anecdotes, making it all flow nicely and having great rapport with the class.

The second part of the Knowledge Review included several dive table questions, and we worked through each and every one of those in detail.

Once that was done, we signed a general liability release and were issued the final test that consisted of 25 multiple choice questions, including several that required the dive tables and a calculator. Those were not idiot questions and required some thinking. Once finished, you joined Rick in the next room where he demonstrated the use of an oxygen analyzer. You then got to use the analyzer yourself and entered the requisite data into a log book, just as you would when you get a Nitrox fill.

After everyone was finished and had done the hands-on with the oxygen analyzer, it was back to the classroom where we went over all the questions. Once again, Rick explained each answer and went into more detail if someone had gotten it wrong. I got 24 of 25 and stumbled over a trivial one. No big deal.

Thing is, unless you really, really goof, you can't fail. You no longer have to hand in the signed knowledge reviews that are part of the course book (and bound in). Apparently, you also cannot fail in the final test; at the bottom is a statement that says something like, "I have gone over the answers I got wrong and now understand the question and how to answer it properly," and then you sign that. And there are no dives involved. So you don't get to experience the difference between compressed air and Nitrox under the guidance of an instructor. No big deal, really, as Nitrox is becoming quite common.

I think I have mixed feelings on this. While Nitrox has been used for a hundred years or so, its use in recreational diving is relatively new. Initially and from what I am told, PADI and NAUI were quite opposed to it. Early course materials included true but rather discomforting statements like "you can die," and even the current course book has sort of a "not invented here" tone to it. It feels a bit like Nitrox is a subject that the certifying agencies were forced to include because the lure of longer bottom times (and feeling better after dives) were such that recreational divers simply wanted to do it.

If used improperly, Nitrox can be dangerous, but that goes for a lot of stuff in life. Anyone can walk into a car dealership and buy a 500-horsepower Corvette or Viper even though such vehicles can be vastly more dangerous than, say a Toyota Camry. There is no "Corvette" certification needed (actually, good thing PADI doesn't run the Department of Motor Vehicles...). So it comes down to common sense.

What makes it all a bit more confusing is dive computers. Sure, understanding the theory behind Nitrox use, and being able to figure out a problem on old-fashioned dive tables, is a good thing, but these days divers rely on dive computers. They may take a look at the maximum depth for their Nitrox mix, but then solely rely on what the dive computer says. And that's a big problem because dive computers are definitely not standardized. It can be next to impossible to even figure out if a dive computer can handle Nitrox unless you have the instructions at hand (and who does?) and that the instructions are halfway intelligible (they often aren't). So you take a class to learn Nitrox diving with dive tables, but then virtually everyone uses their dive computer and may not have a clue how to even set it to Nitrox. A definite weakness in the armor there.

In any case, I am hugely pleased that I finally have my Nitrox certification!

What is Nitrox? There are various definitions. Nitrox is something that almost no one who isn't a diver has ever heard of. And even if you explain it to a non-diver, the whole theory behind it is such that they're likely just going to shrug their shoulders. Hmmm... Nitrox. Interesting. If that.

So what is it? Well, it's a special air mix where the percentage of Oxygen versus Nitrogen is different from that of the regular air we breathe. Regular air consists of about 21% Oxygen, 78% Nitrogen, and one percent of various trace gases (mostly Argon, but also a tiny bit of Neon, Helium, Krypton, Methane and a good half dozen others). Divers generally consider Nitrogen an "inert" gas because our body does not metabolize it. A better description is that Nitrogen is generally inert. There are, after all, things like Nitrous oxide -- N2O -- which is also known as "laughing gas" because of the mild euphoria and analgesia it caused in dental patients. It's also been used as an aerosol in spray cans, and street racers use it to gain more power from their engines as it delivers more oxygen than regular air, and thus allows more fuel to more burned.

None of this matters to divers who do consider Nitrogen an inert gas. Unlike Oxygen, our body does not use it up. However, Nitrogen does play a very important part in diving anyway. That's because it is absorbed into our systems, and that absorption is pressure-related. This absorption is not an issue under atmospheric pressure. Our bodies are in a state of nitrogen saturation, our tissues absorb so and so much nitrogen and that is that. That all changes when the pressure on our bodies is increased or decreased. Decreasing pressure, as in going from sea level up to the top of a mountain where the air pressure is less is rarely an issue as pressure simply goes from one atmosphere, or roughly 14.7 pounds per square inch (psi), to maybe 10 or 12 psi at considerable altitude. It is very different when we dive. The pressure on our body increases by a full atmosphere for every 33 feet of depth. So if we dive down to 33 feet, it is already twice what we experience at sea level, and at 99 feet four times as much. And since dives don't generally last very long, we go from standard atmospheric pressure to several times that and then back within an hour or so.

What does that mean? Well, several things. When we dive, the air we breathe must counteract the water pressure pushing in on our bodies. So at 33 feet, though breathing feels no different, the pressure of the air supplied by the regulator is actually twice that on the surface. We don't really notice that due to Boyle's law that says as gas pressure increases, its volume decreases. The composition of the air, however, does not change. Even under pressure, it's still roughly 21% oxygen and 79% nitrogen. John Dalton figured that out over 200 years ago. Around the same time, another brainiac, William Henry, found that the amount of gas that will dissolve in a liquid is a function of its partial pressure and how easily the liquid absorbs gas. So what do we make of all that?

Well, if we go down to 33 feet, the compressed air we breathe still consists of 21% oxygen and 79% nitrogen, but its pressure is twice as much as on the surface. That means we now inhale twice as many oxygen molecules and twice as many nitrogen molecules. How does the body react to that? As far as oxygen goes, it simply takes what it always takes and the rest is breathed out by exhaling. Even at sea level, humans do not use all the oxygen we inhale in a breath. In fact, it's only a quarter of it or so (else doing mouth-to-mouth resuscitation wouldn't help at all). Down at our 33 feet, we still use about the same number of oxygen molecules, the rest goes to waste (a phenomenon which, of course, is exploited by rebreathers).

Nitrogen, that's another story. As a mostly inert gas it simply gets absorbed into our body tissues in compliance with Henry's law. So as we go deeper, more nitrogen gets absorbed into our body tissues. Not all absorb at the same rate -- some are "fast" tissues and others are "slow" tissues. The software program that I use with my UWATEC dive computer, for example, shows how the various tissue "groups" in my body absorb or release nitrogen during the various stages of my dives.

Now nitrogen, inert though it is considered, does two things. First, while absorbing more of it into our bodies during a descent doesn't do much, releasing the gas again as we ascend is another matter. If we ascend too quickly, the body "off-gases" the absorbed nitrogen in the form of bubbles. If all goes well, those bubbles are tiny and simply go through the blood stream into our lungs where they are safely exhaled. However, rapid pressure decrease can result in bigger bubbles and they can get stuck in the blood and block passages, or they can lodge in inopportune places like joints, the skin or elsewhere. That can have dire consequences. The dreaded "bends" is one. And the bends can range anywhere from discomfort to death.

The second thing nitrogen does is exhibit a narcotic effect if its partial pressure becomes too great. Partial pressure means the pressure the gas represents of the total pressure in a gas mix. Nitrogen's partial pressure is about 71% of the total pressure of air at sea level. As we dive, nitrogen's pressure stays the same in terms of percent, but at 33 feet that 71% is now twice as much in terms of absolute pressure, so we breathe in twice as many nitrogen molecules with each breath. As we go deeper yet, that partial pressure of nitrogen somehow interacts with our nervous system and causes a narcotic effect called "nitrogen narcosis" or, by more poetic souls, things like "rapture of the deep." While that may have its pleasant aspects, being what really equates to being kind of drunk while diving at, say 120 feet, isn't a very good thing.

So this is where Nitrox comes in. When most divers say "Nitrox," they mean air that has a larger percentage of Oxygen and a smaller percentage of Nitrogen. What does that do? Well, with less nitrogen in the breathing mixture, less will be absorbed into the body. If you dive with Nitrox to a certain depth, it's really like diving with air to a lesser depth. Anyone who took the basic open water diving certification classes is familiar with the dive tables. They are about how long you can stay under without having to make decompression stops so that the absorbed nitrogen can be released safely. With less nitrogen, less is absorbed. And that means you can stay down longer. If you stay down the same amount of time as with air, and at the same depth, and then come up, you have absorbed less nitrogen and need less of a surface interval, if that matters to you.

So it's all good, that Nitrox stuff. Well, yes, mostly. But everything comes at a price. With Nitrox it is not only the higher price of a tank refill (they need to create that different kind of air somehow; it cannot just be run through a standard air compressor), but also what another gas can potentially do to us. And that gas is Oxygen. Yes, life-giving Oxygen can also be toxic. How so?

As we go deeper and the partial pressure of Oxygen increases, it can have its own effects on the body. It can make you experience a bunch of syndromes such as tunnel vision, ear ringing, nausea, euphoria or anxiety, dizziness, and twitching or muscle spasms. Those are all warning signs of impending CNS, or central nervous system toxicity. That generally leads to convulsions and you drown. Very bad.

So we have to watch oxygen as well. The partial pressure of oxygen in air on the surface is 0.21 atmospheres. At 33 feet it's 0.42. And at 66 feet 0.63. It's been determined that the maximum safe partial pressure of oxygen is about 1.4 atmospheres, with brief "contingency" exposures of 1.6 acceptable. With compressed air, we get there well past the recreational diving depth limit of 133 feet, so it is not generally an issue when you dive with compressed air. With Nitrox, it's different. Two common Nitrox mixes contain 32 and 36% oxygen. With a 36% oxygen mix, usually called EANx36, we reach that 1.4 atmosphere barrier at just under 100 feet. You can see the problem here, and you can see why divers who want to use Nitrox and take advantage of the longer dive times it affords need to know about all this and the theory behind it. Sure, dive computers take care of it, but you need to understand how it all fits together.

And there's more. While air is air is air, with Nitrox there can be errors. If you think you're diving with 32% oxygen in your tank but, in fact, it's 42%, things can go real bad quickly if you go deeper than you should. So one of the cardinal rules of Nitrox diving is that the diver MUST test the Nitrox mix personally, with an oxygen tester. There are also mandatory records and labels to provide extra safety and accountability.

But even that is not all. Oxygen can be dangerous. It can ignite in pure form, or even when it is present in high concentration. The crew of Apollo 1 perished in a flash fire when a spark ignited the pure oxygen in their capsule. Some filling methods use pure oxygen which is then diluted until the proper mix is reached. So tanks used for Nitrox must be "oxygen-safe." Depending on the oxygen mix, other parts of the equipment, such as regulators, may also need to be oxygen-safe, though the kind of Nitrox recreational divers use does not require anything other than a dedicated Nitrox tank.

So I will soon find out about Nitrox and how it feels. Carol swears by it and uses it almost exclusively. Like many Nitrox divers, she feels less fatigue after a Nitrox dive, and she generally feels better. Me, I have only done a few dives and have not been subjected to to the rigors of lots of repeat dives, so I guess I'll find out.