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Bill, I'm assuming what you mean by "beyond recreational diving on air" is the use of other gases than air such as trimix. If you are using trimix, an air or nitrox computer will serve little purpose since the decompression model is incompatible with trimix. In this case you should get a high quality bottom timer such as what is offered by Uwatec. There is one exception, however, the old Beuchat (made by Uwatec, not Cochran) and the prior generation Uwetec Aladdin Pro make excellent bottom timers for depths exceeding 500ft. It still functions as a depth instrument after you bend it while following your tables; however it may beep you to death. You can unsolder the battery terminal and resolder it to reset it if you need it for a dive before it clears. The newer Uwatec Aladdin Pro appears to work reliably down to about 425ft; you may be able to disable the beeping with the computer interface. I don't know, I don't personally have one. If you find an analog gauge for deep depths, you should have it calibrated. My experience with used analog gauges (such as the SOS 500ft gauge) is they tend to lose calibration and can be off by over 10% (+30ft on a 300ft dive for example). A digital bottom timer is a better instrument as it typically relies on a piezoelectric material, or in some cases a small bender element, rather than a complex mechanism of a squashed bourdon tube, gears, linkage, and needle (which also can be quite temperature dependent if it is not compensated). I have seen several problems with the DiveRite Bridge and Bridge II nitrox computers, to the point I consider them unreliable. Cochran computers look pretty but they also have a bad reputation. I haven't heard much good or bad about the Aladdin nitrox computer. Personally from the perspective of the kind of diving I do, a Nitrox computer offers little utility. I would prefer to dive a set of tables for nitrox. I would look very closely at your anticipated profiles, oxygen limits, and expected bottom times to decide if a nitrox computer will help. They are also expensive. In summary, for diving with trimix use a bottom timer and a wrist watch such as a Casio G-shock. Avoid the Rolex Submariners that "have been deep in Wakula." They don't add any value to your system, or to the watch for that matter. For intermediate dives, consider a Uwetec Aladdin Pro air computer which may serve as a bottom timer for table dives, or as a computer for appropriate air dives. You can pick up a good used prior generation Pro for about $250. Avoid the Bridge, Cochrans and analog gauges. You asked for my opinion. I hope it helps. Doug Chapman -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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