MANY OF US BELIEVED that making trimix computers would be the remit only of small companies with no product-liability insurance that could, should things go wrong, easily close down and open up in the wifes name.
Then diving computer giant Suunto proved us all wrong, by introducing the HelO2. I guess well be seeing a Galileo Stella soon, too!
This has left VR Technology, manufacturer of the popular VR3 and soon-to-be-popular VRX, in something of a quandary. Its a small company that wouldnt want to take on Suunto in a direct fight for a market, but it had to do something. The snappily named NHeO is the answer, and it has been priced accordingly.
If the impressions left by Internet diving forums were anything to go by, all divers are diving on trimix with multiple tanks and wings with stainless-steel backplates.
The truth is that the great majority use nitrox in a single tank with a conventional BC. The folk at VR Technology have wisely decided to address this market, and the NHeO is open-circuit nitrox-ready straight out of the box. It can be upgraded for trimix use later if required.
You can pre-programme in four nitrox mixes for a single dive and switch as you go, so the NHeO accommodates the needs of those who are moving slowly in the direction of technical diving, but are not yet ready for the helium in their mix.
It has full look-ahead decompression built into its algorithm, and as some of us are less computer-savvy than others, the designer has gone for a faster, more intuitive screen-navigation process than with earlier offerings.

As with other computers from the same stable, you need to navigate around the NHeO using a combination of short and long pushes on one or both of two buttons. It takes a bit of getting used to, but most folk soon get the hang of it.
A long push on the left-hand button when in the home screen takes you to the gas list, which enables you to adjust the mixes with which you plan to dive. Choose the most convenient shallow-water stop depth, and add a safety margin.
The NHeO I was lent was upgraded for trimix use with a full-colour screen. Select up to the four mixes, and the maximum operating depth for the chosen PO2 is displayed.

Display Legibility
Warnings come in the form of a large arrow aimed either downwards (missed deco ceiling) or upwards (high PO2) on a red background. Time to surface is shown as a large figure, while actual depth, dive time, deco-stop depth and time are shown in smaller figures.
I found the small figures hard to read at times, not least because of reflections on the pyramid-shaped protective pressure screen over the LCD, which reflected bright ambient light in the shallows. The display backlight seemed less bright than that of its VRX stablemate.

In the Water
In common with virtually every other computer I can think of, this unit powers up automatically when you submerge more than a metre or so.
The NHeO uses a derivative of the standard Buhlmann ZHL-16 algorithm, and all deco-stop dives demand a mandatory deep stop too.
If you pass a stop depth on the way up, the NHeO gives you 60 seconds to get back down to it, or it displays Missed Stops. Use Tables and best-guesses the decompression information.
A hand indicates that your ascent is too rapid. These displays are all against a red background.
The computer also tells you when to switch gases, although you dont have to. In this case, the look-ahead deco calculation will be in error, although the computer will tell you the correct stops when you get to them.
When no mandatory deco-stops are calculated, this part of the screen stays green. When deco-stops are calculated, it turns yellow. In gauge mode, a graph of the dive profile is displayed as it occurs.
When you change to a different mix indicated, you need to tell the computer that youve done it, using a long push on the left-hand switch. You can even add new gases during a dive, should you really need to.

Planning & Logbook
The NheO has a useful simulator mode that enables you to practise using it without getting wet. It also has a dive-planning mode that takes into account the users current residual inert-gas loading. The unit will store up to 22 hours of diving prior to downloading to a PC.
A second screen reveals a graphic profile of each dive logged, while a third screen shows ambient temperature as a profile of the dive. n

Suunto HelO2, £695 without transmitter

PRICE £550 nitrox only, or £605 trimix-enabled
ALGORITHM Modified Buhlmann ZH-16 with mandatory deep stops
FAST ASCENT WARNING Variable by depth
NORMAL IN-WATER DISPLAY Time-to-surface, depth, duration, deco time & depth
PC INTERFACE Factory upgrade
MODES Gauge/Nitrox (multi-gases)
UPGRADES Trimix and multi-colour LCD, CCR-compatible
BATTERY User-replaceable AA 3.7V lithium-ion
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