Dive Computers – Insights for Divers & Professionals. Wolfgang Wild

      (In case the reader should be puzzled by the very special fish which curiously sneaked into the picture – this is a species found only in a lake by the name of “Erlaufsee” in the mountains of Austria: Harryensis endemicus, and it is by no way instructor training staff in camouflage equipment; readers who wish to go diving in this beautiful Austrian lake find the web and email address of dive center owner Harry in the bibliography.)

      As an effort to reconcile everybody, including himself, the following day a new attempt with a different approach was offered. The participating divers should make a short stop during their ascent at 9 meters/30 feet, if necessary adjust their buoyancy, then continue their ascent to 5 meters/16 feet, stop again and adjust their buoyancy again as necessary, and then finally ascend to the surface. (The stop time was irrelevant as the dive time was far from any no-decompression times.) And now, not really surprising, satisfied faces everywhere during the debriefing after the dive. The cozy ambience in the traditional Austrian restaurant “Seewirt”, located right at the lake, with a special cup of coffee with whipped cream contributed to the reviving good mood.

      Occasional contact with participants of this practical field test indicate that a lasting impression has remained which contributed to a sustained change in diving habits.

      One question is still open: What about trying to abide by an ascent rate of, let’s say, 10 meters/33 feet per minute?

      The answer is a practical one: try it, dear reader of this eBook, try it – and have yourself be critically observed by your buddy. „If anyone wants to go slower, they should be encouraged. ... The problem lies not in the theory but in the practice.“ (Richardson, Drew, Slower Ascent Rates, The Undersea Journal, Third Quarter 1988, pp. 5-6)

      Impatient, eager readers will perhaps have the following argument in their mind: But my dive computer does show me if I am ascending too fast, and in addition it warns me with an audible signal. Good objection. Annoyingly at least in the past some dive computers issued such “warnings” – but without any consequences if ignored by the diver.

      “Virtually all of the dive computer user's manuals call for a rate of ascent that is less than 60 fpm, and during our tests, which were all conducted using a rate of ascent of 60 fpm, they beeped and blinked and did everything short of electrically shocking us. Some advise the user to use a variable rate and some of the rates are as low as 20 fpm. Anyone who has tried to achieve such a rate, let alone tried to teach it to a new diver, would be happy to hear that the dive computers performance is not linked to these impractical values. Unfortunately, while we believe that this is true, there is no practical way of testing it.”

      Source: Lewis, John & Shreeves, Karl, The Recreational Diver’s Guide to Decompression Theory, Dive Tables and Dive Computers; Santa Ana, California (USA), 2nd Edition 1993, p. 76

      And the advice for the baffled reader was in 1994 the same as is in 2014:

      “We can do nothing more than advise the reader to contact the manufacturer directly and ask for himself what, if any, requirements are a necessary element of the dive computer's design. Until advised otherwise by the computer manufacturer, you are best advised to follow the ascent procedure prescribed by the dive computer manual.” (ibid.)

      In our later parts Deep Stops – what is that? and Which stop-depth is the correct one? we will come back to this topic once again.

      Excursus – How do divers control their ascent rate?

      As stated above, the challenges during the ascent are quite complex: looking up to the surface to make sure no Manta Ray, boat or the like is blocking your way; ensuring at the same time that your airways are free so releasing excessive air from your lungs is not hindered; controlling your depth & timing device to avoid coming up too fast, and deflating your BCD and/or dry suit – all at the same time.

      Good idea trying this in practice, which we also did (again with instructor candidates). And the voluntary participants in action were of course captured on fotos. Before showing them this undisputable sort of proof some of the participants refused to believe or just denied how they had performed their ascents. A few examples only: Not looking up but rather down to the instrument console with depth-gauge or dive computer; or: in fact looking up and reaching up, with the left hand holding up the BCD hose, ready for deflation – but what about looking at the instrument console or the dive computer at the left wrist?

      The following pictures have been reconstructed with staff members to protect the privacy of the participating instructor candidates; the pictures speak for themselves:

      As can be seen on the pictures there are always practical solutions for both console and wrist models. The diver just has to remember to look up, having everything in his view, including his dive computer, and his airways open. A simple piece of string with a loop attached to the console, and it can easily be hung over your thumb.

      After this short excursion to diving techniques let us now move on to the inner workings of the dive computer.