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April 2004 Vol. 19, No. 4   RSS Feed for Undercurrent Issues
What's this?

The New Wave of Dive Computers

tests find some more readable – and conservative

from the April, 2004 issue of Undercurrent   Subscribe Now

Individual features aside, all dive computers perform the same basic functions. The problem, as the editors of Britain's Diver Magazine put it in their December issue, is that "all decompression theory is exactly that -- theory!" In fact, Divers Alert Network has reported that two out of three divers who had to be recompressed for DCS in the year 2000 had followed no-decompression guidelines and were diving within recommended safety limits. Nearly 75 percent were using computers.

Clearly, some folks are more susceptible to DCS than others. Factors believed to increase DCS susceptibility include age, weight, dehydration, an abnormality of the heart called Patent Foramen Ovale (PFO), and certain dive practices such as repetitive multilevel profiles.

If you want to be cautious, seek out a conservative computer. Diver editors ganged together 11 different computers to make sideby- side comparisons. Taking them beyond the limit of no-stop diving, they could detect differences in their algorithms (mathematical calculations that attempt to keep divers safe from the ill-effects of breathing nitrogen under pressure). They focused just on the decompression information displayed during a dive -- a comparison that can't be determined in a dive shop.

Some computers today call for deepwater stops to reduce the chances of microbubbles forming. The theory is that by reducing the build-up of symptom-free microbubbles during an ascent, less deco time is required in the shallows.Deepwater stops are a relatively new procedure for square-profile divers. However, multilevel divers have been using this approach for years, by making natural progressions up a coral reef, for example. With the test computers ganged side by side, the divers performed the deepwater stops required by some and the long hangs in the shallows required by others, to avoid bending any of them.

The recently introduced Suunto Gekko (similar to the Stinger and Mosquito) and the Dive Rite NiTek He multiple-mix computer proved the most conservative. In most cases the testers felt confident that the mandatory deco requirements displayed were sensible, and they never triggered fast-ascent warnings on any of the computers. "That said," they pointed out, "no one can tell you how close you come to getting decompression sickness or, even more likely, sub-clinical DCS.

"Those computers that seem less cautious might in fact be telling the truth about your decompression status, while the others might just be keeping you in the water for longer than necessary. Or some might simply be more cavalier with your health. We have no real way of knowing." All the more reason to err on the side of caution.

Computer Comparisons

Buddy Nexus: A Finnish model mainly used with the closed-circuit AP Inspiration rebreather, it can also serve as an open-circuit two-gas-mix Nitrox computer. The testers set it for less-cautious "normal" rather than "harsh" conditions. In its "normal" setting it proved slightly more conservative than most of the other computers, but the information it displayed was generally in line with the mainstream. The testers found much of its display too small and too hard to read for serious open-circuit diving. (from $600)

Cochran Commander: The testers set up this model with a maximum 50 percent safety factor to align it with the other contenders. The Commander had a large and clear display and went into deco-stop diving mode almost as soon as, if not before, any of its rivals. But it would often rack up stops at ever-deepening depths, rather than lengthening stop-time at one depth. It then shed those stops on the way up, sometimes prematurely. It permitted "masses of no-stop time available" when most other computers were still insisting on deco stops of five minutes at 10 feet (plus a safety stop in some cases). The testers found it "rather more suited to those who love tinkering with electronic animals" than those who want to get into the water with marine ones. (from $600)

Cressi Archimede: The test computer was faulty and went into "error" mode under water.

Dacor Darwin: Made in Italy by Mares, this computer is bulky. Apart from information being arranged in a slightly different layout on its LCD and slight casing differences, it should perform similarly to the Mares M1 computer. The testers found it necessary to press the mode button much longer than the two seconds mentioned in the instruction book to activate the Darwin. It performed in line with the mainstream, adding a safety stop only after the testers ascended past the 15-footdepth mark -- which was often after it had returned to no-stop diving mode. "We would be confident to use this computer, whether Darwin or Mares M1, to monitor our deco for this type of diving, with the proviso that we treated the safety stops as mandatory." (from $300)

Some computers today call for deepwater stops
to reduce the chances of microbubbles forming.
By reducing microbubbles during an ascent,
less deco time is required in the shallows.

Delta P VR3: The testers found the display hard to read "because there is, quite simply, too much information available." The VR3 allows the user to choose the depth of the shallowest stop computed for. To bring it in line with the other computers the testers chose 10 feet. It requires deepwater stops, some as deep as 90 feet on the 160+ foot dives. When the editors missed one of these stops, the VR3 displayed a large downward arrow and counted down 60 seconds to get there. "If you're not quick enough getting back down to the stop you have passed, the VR3 sulks and will display the words 'Use Tables.'" But even then the VR3 still allowed the tester to use it fully on the next dive. Stops are displayed with the additional graphic of a diver passing up a line to reveal the possibility of continuous decompression within a certain depth range: "quite fun to watch." The deepwater stops properly undertaken meant that the VR3 presented shorter mandatory deco-stop times than some of the other computers once in the shallows. A "good choice of computer if you have the money to buy it and the time to get to know it." (from $950)

Dive Rite Nitek He: This Japanese-made Nitrox and trimix computer "aims squarely at the technical diving fraternity." But the testers used it with an air setting and "obtained results we might have got with its much cheaper little brother, the Nitek." Its display was not the biggest but clear enough. In past comparison tests, the testers found the Nitek to be the most cautious of computers, because it doesn't seem to shed the final minute of a displayed 10- foot stop until the diver actually reaches that depth. In these tests, its algorithm "seemed to be either the first or second most cautious." "A sensible choice for this type of diving." (from $1,100)

Mares M1 RGBM: Identical in every other way to the Dacor Darwin and Mares M1, the new Italian-made Mares M1 RGBM uses a modified Mares algorithm to put in optional deepwater stops, and thereby credits the diver with less time required in the shallows. The M1 RGBM returned to nostop diving mode a couple of minutes before its more traditional sibling, the Dacor Darwin, on every dive. (from $330)

Oceanic Veo 250 (also Versa and Versa Pro): This new U.S.- made computer proved easy to read and simple to set up by means of its two-button menu-system. It offered information on necessary deco-stops completely unlike the other computers. It went into deco-stop diving only below 160 feet, some time after all the other units sitting alongside it and was generally back into nostop diving as soon as the testers reached 30 feet. The amount of no-stop time then offered seemed "enormous" in comparison to the others. The editors found that the Veo 250 "revealed a Jekyll and Hyde character in that at times it seemed to be working with two entirely different algorithms." They concluded: "We cannot say that it was either too cautious or incautious because we could never anticipate which of the two it was going to be." (from $350)

Scubapro Uwatec Smart Pro (also Smart Com): This Swissmade computer was the subject of a recent recall, reported in the August Undercurrent. The instruction manual offers little in the way of guidance as to which of five levels of microbubble suppression anyone should use, so the testers activated the setting "Micro-Bubble Suppression Level 1." The display gives lots of information, laid out in a very easy-to-read way. What the manufacturer calls "level-stops" were always called for at 20 or 10 feet, which seemed no different than extended deco stops. The testers suggested that new users set it at micro-bubble suppression level 2, where level-stops might be displayed at more obviously deeper depths. "Setting up the computer needed a little intuition, not to say dexterity, as it had rather oldfashioned wet-finger contacts, and the important setting-up icons were very small." Unlike the other computers tested, the Smart Pro does not have a user-changeable battery. (from $500)

Suunto Gekko: The Gekko uses the same Suunto RGBM 100 algorithm as the Stinger, Mosquito, and Vyper. The editors found it "probably the most conventionally conservative of all the computers tested here, with long stops at 10 feet consistently indicated on every dive." They set the Gekko for its least cautious mode or "personal setting," and its clearly designed display indicated total-ascent time and stop-ceiling depth when in deco-mode. It also adds in a threeminute safety stop in the shallows, once up past 20 feet (included in the total ascent time). (from $350)

Suunto Vytec: This top-of-theline Suunto offers computations using three different Nitrox mixes which are easily changed during a dive. It can gas-integrate, with Mix 1 giving tank-pressure display and calculated remaining air-time with the aid of an optional high-pressure transmitter on the regulator first stage. It also gives the option of both Suunto RGBM 100 and the less cautious Suunto RGBM 50 algorithm, which the editors used for their comparison. Still, they found, "there seemed to be little difference to the decompression required by its similarly set sibling Gekko (RGBM 100), with only about one minute in 10 being shed from total deco-times even after a long series of dives in the 160+-foot range." The testers found all Suunto computers "very user-friendly, with easy-to-set-up and clearly understood displays." (from $850)

Note: U.S. prices listed here are approximate starting points. Options such as PC interfaces can increase prices considerably. Most are distributed in the U.S. but may not be in your local dive shop. In such cases, you'll have to order them through international mailorder catalogs or through e-tailers.

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