• Lip-smacking but not finger-licking - Mares Guardian computer
• Yellow, green and too wet for comfort - Seac Sub ZX 3000 Nitrox
• Design for a simple life - Oceanic data 100
• Mother-in-law of invention - Fox 40 whistle

WITH the exception of air integration and audio (speaking voice) mode, the new Guardian dive computer has all the features offered by other computers in the Mares range - plus a few of its own.
This chunky item, packaged in a smooth, anatomically designed case, has a clear display with probably the largest figures I have seen. As a full-function decompression-stop diving computer, it immediately distinguishes itself from the competition by being controlled by a combination of three push-buttons rather than the more common wet contacts. So no more frantic finger-licking between dives.
Another feature that makes this instrument unique is that it runs on three ordinary AAA alkaline batteries, which are easily obtainable anywhere in the world. These are contained within their own integral watertight compartment, so if you foul up when replacing them, allowing dirt to reach the water-sealing O-ring, the batteries may get wrecked but the computer will not. Also, the computer does not lose a diver's off-gassing information during the battery change. User-replaceable AAA batteries allow you to use the illuminated display with impunity during night dives or periods of poor visibility. The backlight is so bright that you could virtually use the display to find your way. By pressing the correct combination of buttons you can either have it on for a few seconds each time you want to read it or leave it on permanently. Goodbye to glow-sticks and any fear of your computer battery going down during a long trip away from home. A set of AAA batteries should last about 100 hours of normal diving or 25 hours with the backlighting permanently switched on.
As soon as you hit the water, the computer switches to dive mode. It can tell the difference between fresh and seawater and automatically calibrates in this change even if it happens during the dive, for example in a cave system. It also takes the water temperature into account in its algorithm.
While you are underwater the computer displays remaining no-stop time, depth, dive-time, water temperature and maximum depth achieved. If you require deco stops, it shows the depth and time of the required stop, and the water temperature is exchanged for a total safe ascent time. The usual upward and downward triangles prompt the diver to take the best course of action. A graphic ascent-rate indicator with an audible alarm controls a variable rate from 18m/min up to 20m deep, and down to 10m/min between the last 10m and the surface.
The Guardian uses a modified Haldanean-type algorithm (nine-tissue model with half-times from 2.5 to 480 min) with additional input from the work of Dr Spencer in the USA. You might think this is less sophisticated than the latest Swiss Buehlmann algorithm, but using the Guardian extensively alongside the latst Aladin, I noted that the information was not that different.
Sometimes the Guardian gave longer remaining no-stop times and at other times shorter. When I got into deco-stop mode it was the same story. However, if you do a long no-stop dive with the Guardian, and come back to 5m with an ample 99min of no-stop time remaining, it will still switch into safety-stop mode as the 5m barrier is breached and indicate "St3" in large figures, meaning stop for an additional three minutes.
Unlike those computers that automatically sense ambient barometric pressure, the Mares Guardian leaves you to select one of four programmes. This lets you select your own degree of caution (or make your own mistakes). I used the Guardian in its least cautious mode.
An additional feature of the Guardian is the UBA (underwater behaviour analysis) display. This reports any unusual or foolhardy diving profile by means of five possible "bad marks". These come up if the diver misses a deco stop, has an uncontrolled ascent, dives within two hours of the last decompression stop dive (I confess to seeing this displayed), dives deeper than 40m (sorry, I got that one too), does a repetitive dive deeper than the previous, or a repetitive dive deeper than 30m, or an excessively fast ascent.
These signal marks are there for the dive marshal to see and they stay until the next dive. The Guardian also has a clock mode which will tell you the time and date, rather like an over-sized watch. This information is logged with each individual dive.
Other settings allow the diver to select the degree of caution and also to clear off the memory. The latter would be useful for dive shops or schools that may wish to hire out the unit with no memory of the previous user's activities. You can also choose whether to use metric or imperial units of measurement.
Like all top-of-the-line computers, the Guardian can be used for complex dive planning when in simulator mode. Naturally, there is a log-book function and the unit can be interfaced with a PC after the dive.
I found the desaturation-time and the time-to-fly displays slightly confusing, as the latter was always greater than the former. As yet, I have been unable to unravel this mystery. The Mares Guardian costs £330.

Blandford Sub-Aqua, 01923 801572

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Yellow, green and too wet for comfort
Many regulators now on the market are compatible for use with nitrox at less than 50 per cent oxygen. However, we are now beginning to see the arrival of regulators dedicated to nitrox. These are usually distinguished by their yellow and green colour scheme, which is helpful for those who might be using nitrox as a deco gas, avoiding as it does confusion between different second stages during the dive.
The Seac Sub ZX 3000 Nitrox is typical of this new breed and last September I received an example, complete with octopus, to try on Diver's behalf.
The regulator looked well finished, and I was confident enough to take it with me on a Caribbean trip with an extremely heavy schedule of dives.
I planned to use a nitrox mix in conjunction with an "air" dive profile, to give me an added margin of safety over air. By the end of this series of dives, my 30 hours-plus of residual nitrogen level, as calculated by my "air" computer, made these safety gains worthwhile.
That part of my plan went well. However, things did not go so well with the regulator. Rarely do I encounter equipment with which I am not happy to dive. If there is a problem, I am usually able to adapt my technique to overcome it. Not so in this case.
My first dives with the Seac Sub ZX 3000 Nitrox were very uncomfortable, because I was getting such a wet breathe. It seemed that if I looked down (towards my camera), or indeed turned my head in any direction other than straight ahead, water entered the second stage. I persevered until I found myself diving in a strong current off Klein Bonaire, and seemed to be getting more water than air. When I returned to the main island of Bonaire, people were remarking on the unusually low tide. I was not surprised. I felt I had drunk most of the ocean during the previous hour underwater!
When I returned to Britain in February I was greeted by a message from Stephen Muirhead of Seac Direct (UK), asking me not to test the regulator he had sent in.
He told me that I had received a pre-production prototype and that the manufacturer was working on modifications to both the first and second stages, including the mouthpiece. I told him about my own experiences and he said he would report back to the maker.
Clearly Seac Sub has some work to do, but I look forward to testing an improved version of the ZX 3000 Nitrox - and, I hope, an example of the standard ZX 3000 model - at some point in the future.
In the meantime, if you find yourself in possession of a rare example of an early version of this regulator, I suggest that you avoid using it, other than in the safe confines of a clean swimming pool.

Seac Direct (UK) Ltd, 0114 270 1234

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Design for a simple life
THE Oceanic Data 100 computer, like the earlier Prodigy, will appeal to those who want good value and complete simplicity of operation.
The Data 100 uses a modified Haldanean algorithm with a database by Rogers/Powell, incorporating Spencer's M values in 12 tissue compartments from 5 to 480 minutes.
It might sound complicated, but in use it is simplicity itself. All you have to do is remember to turn it on before entering the water.
The major display shows remaining no-stop time. Smaller displays show depth, maximum depth, and dive duration. A graphic "tissue loading" bar graph creeps round the dial as your no-stop time reduces, and once it gets beyond the green zone into the yellow caution zone it is time to ascend.
If you let the graphic display reach the red zone, you are deco-stop diving. Each section of this zone represents a stop depth (in increments of 3m to 18m) beyond which you should not go until the graphic has moved back into a shallower zone. This information is augmented by a flashing decompression dive mode icon.
At the same time, the display alternates between current depth and the required stop depth and time, along with maximum depth achieved and the dive duration. Explanatory icons keep you in touch with what you are looking at.
As you ascend, a further graphic "variable ascent rate indicator" lets you judge your progress. By keeping it out of the red section you know you are rising at less than 18m/min.
So with the Data 100 all you have to do is keep the graphic displays in the green and everything should be all right. When you are out of order, things will start to flash.
The computer has an effective backlight feature operated by pressing the activation button during the dive - useful in low light or night-diving conditions. It also remembers details of the past 12 dives, counts down the time until you can safely fly from 24 hours after the last dive, and will scroll possible safe no-stop times and depths between dives.
Compared to more sophisticated computers like the Mares Guardian or the Aladin Air (next month), it was clear to me that the Data 100 was less cautious in its calculations. In fact it always gave me a considerable amount of extra no-stop time.
For those who want a simple and inexpensive computer to use in warm clear water, and only infrequently for deep diving, this could be it. It uses two user-replaceable shirt-button lithium batteries that should last for at least fifty 24-hour periods of diving. It costs £213.

Oceanic, 01404 891819

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Mother-in-law of invention
Have you ever found yourself at the surface in sight of your cover boat but been unable to attract anyone's attention?
So often the occupants seem to be looking studiously in the wrong direction. And it is amazing how the sound of waves and a boat's engine can drown out the shouts of divers in the open sea.
Referees must have a similar problem trying to get the attention of offending players when they are up against the roar of a Wembley crowd. How do they do it?
Enter the Fox 40 whistle. Invented originally for Canadian ice-hockey referees - who experienced problems with their pea freezing or icing up - the Fox 40 has found favour with the US Coastguard, NATO forces, the National Basketball Association, FIFA and seven other sports that were featured during the recent Olympics.
In a test situation, I found it even brought my mother-in-law to a silent halt from full flow, at a distance of 40 paces!
The Fox 40 is loud, has no moving parts, glows in the dark and costs around £4. It is now available in most marine and diving shops.

Markat, 01935 815424

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