Teaching Tips: Personal Dive Computers

By Steve Lewis

We get a considerably varied and pretty constant stream of email into our office from divers across North American and from around the world. Sometimes it’s to tell us how pleased they are about the service they got from one of you folks. Sometimes it’s to ask about the quality of diving in some far-flung corner of the Pacific. Occasionally it’s a complaint. But from time-to-time we get asked to explain why we do things the way we do, and these are usually the most fun to answer!

Last week, I got a message from off one of the many scuba-related forums on the web that we monitor. Apparently this diver’s girlfriend had signed up for an open water course and he was shocked to learn that his local dive store had switched affiliations and was now promoting, what his old instructor termed, “SDI’s superior program!”

That happens more and more these days… but he asked what the differences were between the Open Water program he had taken through another sport diving agency and SDI’s. He explained that he was shocked to learn from his girlfriend that SDI promotes the use of personal dive computers (PDCs) rather than making students work through calculations using tables.

During one of our conversations, he said he felt she was being short-changed and that not learning tables was dangerous. He actually said “if sport divers or occasional divers can’t familiarize themselves with the tables then should such an unsafe person be diving?” Frankly, I was a little floored because it seemed to me he was telling me that ALL SDI-trained divers are unsafe, because their instructors have not made them slog through an antiquated system that most divers forget how to do unless reminded on a regular basis.

For the record, let me share with you want I explained to him because you too may run into someone who harbors similar misconceptions, and although I am sure you have your own version of things, the explanation that follows may help you sometime in the future.

Let’s start at the beginning. SDI is different to the other major sport diving agencies because it was created by people who ran a technical diving agency; the biggest technical diving agency in the world, TDI. The men and women who helped put together its curriculum and developed its courses had the strongest background possible in diver education and diver safety, and the attendee list of those early brain-storming sessions read like a who’s who of recreational diving… both technical and sport branches.

Their primary concern was to create an open water course that made diving an adventure rather than a chore, and one that had a sort of “sky’s the limit” perspective on diver education… after all, many of those early SDI instructors had experience exploring exciting spots around the globe that few divers had ever seen. The majority of them had been teaching people to dive in caves, and running diver programs to depths about three-times the “normal” sport diving limits. So their perspective on how far a student could progress was a mite broader than instructors from other backgrounds!

Right from the beginning, SDI brass determined that all SDI-level divers wear a personal dive computer. In the simplest terms, this determination was driven by safety, and not as my correspondent suggested collusion with the dive computer manufacturers! Personal dive computers have evolved immensely since the first brick-sized units available in the 1980s. They have become easy to read, understand and use. Their functions go way beyond those offered by their predecessors… for example, downloadable graphic dive profiles, and logbook functions. And, most importantly, they are the best tool currently available for controlling ascent speed… something we believe needs to be managed because of what seems to be a very strong association with bubble troubles.

Of course the core function of a PDC is to track average nitrogen loading in real-time and give a good approximation of the decompression status of the person wearing it minute by minute (actually, second by second in many cases). Because of this, among other benefits, a savvy diver is able to maximize her bottom time while keeping within the No Decompression Limits of her dive. No table can come close to this level of accuracy and, by inference, offer comparable security. The mitigation of DCS is never zero regardless of what method is used – tables, PDC or some other Voodoo – but for sport divers, a PDC is without comparison.  In short, a PDC is an extremely useful tool within the budget of the majority of sport divers.

Of course the one important proviso is that when a SDI diver graduates his or her open water class, their instructor has helped them to understand the computer’s functions and benefits, and they have been encouraged to read the user’s handbook and discuss anything they did not immediately understand.

Now on the topic of tables. We do not discourage instructors from teaching tables, in fact all our leadership courses (DM, AI, OWI, SIT, IT) have components where the US Navy, DCIEM and Buhlmann tables are used, but extensive research has told us that sport divers and tables do not mix well. In fact, there are strong indications that unfamiliarity with dive tables among occasional divers keeps people away from diving. Because of this and other concerns about table use on multiple dives, CNS tracking and related issues that may have a negative effect on a diver’s well-being, we discourage tables as primary information.

The arguments for tables actually remind me of the arguments that are offered against technological advances in all forms of sport and pastimes, not just diving. I’ve heard people rally against seat belts and anti-lock brakes, airbags and traction control in cars. (Actually, members of my father’s generation despised synchromesh gears!) But of course these innovations are now standard in any late model car. They save lives!

The vast majority of ski hills don’t allow skiers on their slopes without modern bindings and boots. Leather and duct tape are no goes.

The list goes on and in our industry, there are many of you who may remember the cries against SPGs, BCDs and things that we take for granted now. The old way is NOT the best way, and thinking that tables are somehow superior for sport divers is simply nonsense.

Forgive the personal note but my wife, a smart woman in all but her choice of life companion, was terrified of tables when she first learned to dive. It was not the math or the process that scared her, she’s an executive with one of the largest hotel chains in the world and deals with numbers and process-driven protocols every day. What scared her was getting it wrong. She felt the penalty for a mistake using tables was so severe, she was reluctant to dive. A computer solved that problem… now if I can just get her to master the reverse frog kick…

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