EXTRA

HEAD to HEAD:
CRESSI ARCHIMEDE V MARES M1




Two new diving computers from big names in Italian dive gear are aimed squarely at Suunto Vyper territory. John Bantin reckons they provide a good demonstration of the current state of computer thinking

Archimedes' Principle: When an object is immersed or partially immersed in water, the loss of weight of that object equals the weight of the water displaced. The popular myth is that the Greek physicist Archimedes discovered the principle of buoyancy while sitting in his bath, and was consequently seen running down the street shouting: "Eureka!"
     The Cressi-sub Archimede is not the result of such a startling discovery, more the consequence of close study of what every other computer manufacturer has been doing. It's a Japanese-style approach to product development, and the electronics of the Archimede apparently come from Japan.
     If the now-discontinued Mares Tutor and Surveyor computers were the Preston By-pass, the latest Mares computer is the M1. After experimenting with small-scale production of computers using bought-in parts, Mares has finally gone all the way and designed a diving computer wholly made by the company at its plant at Rapallo in Italy. It's called the M1.
     Both these new computers will inevitably be compared with the Suunto Vyper, part of a family of computers which at present dominates sales worldwide, and this has been borne in mind in making this Head to Head comparison.
     The last thing you think about with a computer is the way it will interface with a PC to download the dives you have done. Mares, however, thought of this first, because the particular method used with the M1 comes in useful during the manufacturing process.
     The computer and interface communicate via an infra-red signal emitted by the computer. The IRIS interface, a modern executive-toy-like device, has only to stand near it rather than be connected to it.
     How does this help in manufacturing? All computers need to be calibrated, and this usually means an operator observing the displays of groups of computers as they are test-dived in a pressure chamber. There is a limit to how many computers one operator can watch at one time, so the occasional bad one is likely to slip through.
     At the Mares factory, however, they can gang up 48 computers at one time in a pressure chamber and they can communicate with infra-red sensors outside the glass. These sensors in turn are linked to one mainframe computer that can interrogate each diving computer. Roberto's your uncle!
     Mares has derived a lot from the design of the Tutor and Surveyor, including the use of two readily available AAA batteries, as well as concluding that the best policy is to make every component in-house.
     The Archimede, too, has a user-replaceable battery, a popular lithium CR2032. The computer looks very similar to the Suunto Vyper in shape. Like the Vyper, it is also operated on the surface by three buttons. The Mares M1 uses only two buttons but in other ways is also reminiscent of the Vyper. Let's hope we've seen the end of those frustrating finger-licking sessions for good!
     When it comes to appearance, if the Vyper is a solid-looking Scandinavian Volvo, the Mares is a sexy Alfa Romeo and the Archimede the equivalent of a smooth and functional Honda.
     Like the Vyper, both the M1 and Archimede are menu-driven, operated by push-buttons and programmable for nitrox mixes up to 50 per cent. You can choose a maximum PO2 from 1.2 to 1.6 bars with MOD alarms to match. Like the Vyper, the M1 is also useful as a bottom-timer for tri-mix and free-diving.
     The main difference between the Archimede and the Vyper is that the Archimede uses the nine-tissue-model Buhlmann ZH-L16 algorithm with tissue half-times from five to 640 minutes. It's a sister algorithm to that used in the long-running and undeniably successful Scubapro Uwatec range of Aladin computers. So it is, if you like, aimed at those who like the physical Vyper features (the Vyper uses the unique Suunto RGBM algorithm) but prefer the Aladin-type mathematical calculations.
     It is not clear which algorithm the MI uses. It is said to be "an 11-tissue of the exponential-deterministic type, with M values derived from the work of Rogers and Powell". In practice I found the Archimede and the M1 almost identical in the no-stop times and deco requirements displayed.
     Mares has done away with wet-contacts entirely. You can turn the M1 on before you hit the water or allow it to turn itself on automatically. Should you choose the second route and hit the water just as it's busy doing its self-check, you can still turn it on manually under water.
     A useful touch is the mineral glass front, which is rather more scratch-resistant than the plastic more often used, so no secondary display guard is required.
     The Archimede turns on when you hit the water. When it gets to within three minutes of no-stop time remaining, it peeps a warning and its bright display illumination flashes.
     Like its rival, once into decompression-stop diving it shows the depth of the first stop, stop time, and total ascent time. There is a bar-graph for both nitrogen-loading and oxygen-loading. Ascent-rates are variable according to depth and can be monitored against a further bar graph. Violations of ascent rate or stop-ceilings are indicated again by warning peeps and the display illumination flashing.
     All three computers also automatically build in an additional safety stop between three and five minutes at between 6 and 3 metres. Because the Cressi would go to its safety stop at 6m but the Mares waited until I was at 5m, the Mares was always the slower to clear, but when I did deeper deco-stop dives, it was the Cressi that seemed slightly more conservative.
     Unusually, dive times on the Mares M1 are displayed in minutes and seconds. This is useful when using it in free-diving mode, and for diving it's nice to know just how much of that remaining stop-time is in seconds, too. There are four manually selectable altitude programs which double for those who want to add caution at sea-level. The M1 can be set for either fresh or sea water. Those familiar with the Tutor or Surveyor will find many similarities with the display.
     The Archimede has probably the clearest display of any computer available. This instrument automatically senses and selects one of four altitude settings and, in addition, different degrees of caution can be pre-selected.
     Both these new computers have all the traditional diving functions, including a timed backlight display that can be adjusted for duration. Deco-stop times and depths are displayed alongside the total ascent time, and ascent rates are variable. The speed of ascent is shown as a percentage of what is allowable at that depth with the M1 or as a segmented display with the Archimede. The Archimede has an unmissable SLOW and STOP message that can show during ascents.
     As we have come to expect, when not performing the functions of a diving computer both these units double as a calendar and watch. The M1 has four manually selectable altitude programs which double for those who want to add caution at sea-level. It can be set for either fresh or sea water.
     The Cressi-sub Archimede costs £299. The price of the conventional PC interface was not available as Diver went to press. The Mares M1 comes in cheaper at £250, and its IRIS interface and software costs £69.50.

Blandford Sub-Aqua 01923 801572, www.blandfordsubaqua.co.uk