The Cochran Commander Nitrox is a 2 mix computer, suitable for use with accelerated deco, despite the manual giving warnings that it is not intended for decompression diving! It can be used for trimix diving as if it gets 'bent' it goes into gauge mode and will still give correct depth/time information.

Housed in a green plastic airtight case, the Cochran has a large clear display. A backlight with a dull red glow can be turned on before the start of the dive, which is very useful for low light conditions; it's a shame however that the light can only be turned on and off in program mode, i.e. not under water. The backlight obviously runs the batteries down quicker, but this is not a big problem as the batteries are user-changeable. Programming is achieved via 3 contacts on the right using the standard tool, an American 'Quarter'.

In program mode the first and second gas mixes can be set, to an accuracy of 0.1%! The third parameter to be set is the 'bottom time'; if the dive time is less than this the computer will not switch to the second mix on ascent, e.g. if the dive is aborted. Setting a very long bottom time effectively turns the computer into a single mix computer. The fourth parameter is the depth at which gas switching to the second mix is assumed to take place. The fifth parameter is the amount of user-added conservatism, from 0-50%. The final two parameters are whether to turn the backlight on, and the depth at which an alarm is sounded. Using the PC interface several other parameters can be set e.g. whether the decompression algorithm is adjusted for water temperature, what ascent rate warning you want, what the sampling time is (from 1 to 16 seconds).

In practise the computer is easy to use and has not failed once in two year's use of nitrox and trimix diving, despite some ugly rumours about the reliability of Cochrans. The algorithm appears to track reasonably well with Buhlmann tables, and I tend to run it with a conservatism of zero. Up to no-stop times it gives a very similar no-deco time to my Suunto Solution Nitrox computer. Beyond that though the Suunto tends to pile on the deco quickly while the Cochran seems to add it more closely to what I'd expect from tables. I plan deco dives from tables (DDplan or similar) so I don't tend to go with it's deco predictions, however.

The PC interface is reasonably straightforward although it would benefit from a rewrite to make it windows-compatible - the gui is truly appalling. It does give you all the information including depth, ascent/descent rates, ppO2, temperature, CNS clock etc. Some of the computer's programmable parameters are only settable from the PC interface, so for serious use it's essential. A wealth of information about the dive, statistics about the dive etc. can also be accessed.

The only big problem is that there's no UK dealer any more!

(c) Keith S. 2002