IT WAS THE FINNISH COMPUTER COMPANY Suunto that first made inroads into the market. Called the Spyder, its deco computer that doubled as a watch proved very popular, despite its digital time display.
Back in the late 20th century, watches with digital displays were seen as cheap alternatives to those with hands. There wasn’t even a word for traditional watches, what we now call “analogue” displays. But digital watches caught on.
Suunto soon improved its product with a nitrox capability, and the Stinger was born.
Meanwhile, other dive-gear manufacturers headed to Seiko in Japan to source a computer-watch of their own, and models emerged bearing a selection of well-known brand names, but they never threatened Suunto’s market dominance.
Now there is a plethora of computer-watches from which to choose, not least because Seiko appears to have withdrawn from the sector, so many big-name brands have had to source their own computers closer to home.
If you’re going to develop a diving computer, why not make a computer-watch variant too
If Suunto still dominates in Europe and Asia, Oceanic’s associated company Pelagic has developed attractive propositions that prove most popular in the Americas. And Scubapro and Mares have crashed onto the scene with their own ideas of how it should be done.
Each computer-watch included here is worked using four buttons. All offer Gauge mode if you simply want a time/depth function. In all cases the menus are quite intuitive.
There is a myth about computer-watches – a suggestion that because the unit is small the display is difficultl to read, or that you don’t get a full spectrum of information.
By way of example, however, the dot-matrix display of Suunto LCDs gives figures as big as on any full-size computer.
You need to push a button to get peripheral information, but all the crucial stuff is there, loud and proud.
Most computer-watches require an extension strap to fit round the wrist of a drysuit.


NOT TO BE OUTDONE by the sudden arrival of rival computer-watches, Suunto offers gas-integration by radio transmitter as an extra-cost option with its three models. Oceanic is hard on its heels.
These gas-integrated computers not only tell you your decompression status and current tank pressure, but calculate how long that gas will last at your current depth and at the rate you’ve been breathing it.
You can program in a reserve pressure, too. If you keep your remaining gas time longer than your total time to the surface, you shouldn’t get into trouble.
Let’s lay to rest some of the myths surrounding these magical bits of kit:

  1. Your camera’s flash will not cause the computer to lose the transmitter’s signal. This might have happened with early radio-linked computers, when used with a flashgun that employed an electronic vibrator to indicate recycling of the capacitors, but underwater flashes haven’t used those in years.
  2. You get a tank-pressure display as well as the gas-time prognosis, so you are always aware of the basic information.
  3. There are fewer O-rings to offer failure points than in a hose/pressure gauge.
  4. Radio has been proved reliable. Everybody uses it! 

Drawbacks Well, you have to get the battery in the transmitter changed every few years. You could do this yourself, but manufacturers have proved that not all divers are sufficiently dextrous.
Screwed into the regulator first stage, the transmitter looks like a convenient handle for a boat crew-member when hauling a tank on board.
Yelling “don’t hold it by that!”, the first time it happens helps develop muscle memory for such crew, but you can save a lot of anguish if you stick one at the end of a traditional high-pressure hose.


WE ARE TOLD THAT the latest pressure sensor employed by Suunto offers a far more accurate depth measurement than before, and must take their word on that.
Deep stops can be selected on the D4i and D6i, although a diver can choose to ignore them when the time comes, so I guess these are just an add-on and not crucial to the algorithm, rather like the three-minute safety stop at 5-3m.
Now you get both stops displayed, rather than one or the other as before. You used to have to pre-select one or two minutes as a deep stop, but now the algorithm calculates what is appropriate, and credits you in the shallows.
Countdowns are now in minutes and seconds, which is more comforting than displaying a one-minute stop when perhaps only 25 seconds is required.
Sampling rates are increased to a choice of seven, from every second to every minute.
Actual surface interval is also now displayed between dives, and time-to-fly has been relegated to an icon. The memory logbook shows average as well as maximum depth achieved on a dive, and there’s bar-graph representation of the dive too.
When it comes to the gas-integration option, the new range of Suunto computer-watches pair permanently the first time, and unless you choose to change a transmitter code because, for example, another diver on your boat is using the same one, they stay paired.
The electronic compass display, once switched on, stays on until you’ve finished with it – unlike the annoying compass of the old D6. Now it is 3D tilt-compensated too.
Detailed graphical logs and dive data can be available on your laptop using Suunto DM4 software.
All Suunto computers use a Wienke RGBM (Reduced Gradient Bubble Model) algorithm that kicks in with repetitive dives.
The new-sounding alarms aim to evoke what it is they are trying to tell you. For example, if the computer thinks you should be going up, you hear a series of beeps with a rising note, and vice versa.
There is also a different beep for gas-switch alerts. However, when wearing a hood you need very good hearing to notice these audible alarms.
Many people will confirm that the RGBM algorithm is punishing for repeat dives. Some even complain about it. The old D6/D9 had the option of RGBM100 or the less cautious RGBM50 to counter this criticism, but the most recent models don’t have this feature.
However, my own tests reveal that the the latest D6i is less cautious than the older D9, which also gets more cautious with subsequent dives. At one point during repeat dives, I had 20 minutes of ascent time displayed on the D9 while the newer D6i was still giving a no-stop display.
From this I deduce that the latest Suuntos are less punishing with repeat dives.
Alas, all the technobods in Finland were away on holiday at the time of writing, so you’ll have to take my word for it.

Suunto D4i £645
(£395 without transmitter)

Entry level but gas-integrated.

This may be the entry-level model of the three Suunto computer-watches but it is very capable. The deep stops displayed are iterative in that you can ignore them if you wish without further deco penalty. Enabling deep stops no longer disables the safety-stop display.
The D4i has a technopolymer case trimmed with stainless steel and is depth-rated to 100m.
It is available with a strap in a choice of various colour schemes and with the option of a black anodised trim.

Suunto D6i £875
(£625 without transmitter)

Up to two nitrox mixes per dive.

The D6i, in its stainless-steel case, looks slightly more robust than its cheaper sibling. It can be programmed for two nitrox mixes per dive, as well as being usable in Freedive mode.
It is depth-rated to 150m. Stopwatch mode can be activated during the dive.
A stainless-steel bracelet, a sexy black version (with black elastomer strap) and a fetching white version with a white silicone strap are options, all with scratch-resistant sapphire glass faces.
Of all the computer-watches featured here, the D6i in standard, black or white is probably the most acceptable instrument to wear as an everyday watch.

Suunto D9tx £1195
(£945 without transmitter)

Trimix or nitrox in multiple mixes per dive.
Gas-integrated to one tank.

It’s as bulky as its predecessor – that is, hefty for an everyday watch – but uses the same Suunto/ Wienke algorithm as the Helo2, differentiating it from the D4i and D6i. You can add a helium percentage, making it the only computer-watch suitable for use with trimix.
You can preset up to eight gas mixes with 21-99% oxygen and 0-92% helium. Unlike its siblings, deep stops displayed are mandatory even when used in simple Nitrox mode. Depth rating is 200m.
The D9tx may have the same dimensions as the older D9, but the titanium case has a serious gunmetal finish and less bling. Like the D6i, it features a Stopwatch mode that can be activated on the dive.
My only complaint is that the strap is not made of the same material as on its siblings and the extension strap is made of a different elastopolymer – it proved difficult to thread through the buckle-loop over a bulky drysuit-clad wrist. A titanium dress bracelet is optional.
The D9tx comes with a USB interface cable for downloading dives to a PC.


US-MADE COMPUTERS were traditionally aimed at warmwater leisure divers who didn’t go very deep, and tended to be out of the water quickly, asking to go somewhere else.
The algorithm was accordingly aimed at no-stop diving in less than 30m. Unfortunately distributors in other countries insisted on trying to sell these computers to divers with different diving habits, in which case the Jekyll & Hyde instrument defaulted to a vindictive table that would really punish them for going beyond its simple parameters.
Oceanic computers now come with both algorithms, so you can opt for either the old Pelagic DSAT no-stop diver’s algorithm, or the new Pelagic Z+, which appears to perform much like the algorithm familiar to divers in Europe. The only problem I foresee is that owners must choose which algorithm to use, but perhaps astute retailers will set it for them.
The Pelagic Z+ uses the Buhlmann ZHL-16C database, which Oceanic says meets demands including repetitive diving, coldwater diving, deco-diving and diving at altitude. That may be true, but it’s much more in line with other computers.
Setting up is done by a long push on the Mode button, and using the three other clearly marked buttons for navigation and selection.
Menu Set A is for setting the alarms. Menu Set U is for things you are unlikely to change often, such as the units, wet activation, algorithm, conservatism, sampling rate and, unusually, the deep stop function, which I tend to change according to the dive.
Menu Set F is for the nitrox percentages, and you can set up to three mixes for one dive.

Oceanic Atom3 £750
(£473 without transmitter)

Integrates with multiple tanks.

The Atom is a top-of-the-range three-mix nitrox computer in a wrist-watch format. It is wirelessly gas-integrated by means of a radio transmitter that fits to the high-pressure port of the first stage, but Oceanic also offers the facility to integrate the computer with all three gas supplies being breathed, provided you employ three separate transmitters.
The standard Atom with one (dark grey) transmitter is intended for the primary supply, but both yellow and green transmitters (for high levels of O2) are available as optional extras.
The battery is user-changeable, without losing any data, and PC download software and a USB interface cable are standard. The same interface system can be used to upload settings that can change the main time and date, set alarms and adjust various utilities such as changing the sampling rate and transmitter link codes. These last can also be set using the computer buttons.
The Atom is a full-function decompression computer, but in surface mode works as a typical digital calendar/watch/chronograph, with a dual-time function. Four buttons are used for setting it up.
You can set any nitrox mixes between 21 and 100%, and vary the PO2 alarm setting from 1.2 to 1.6 bar using three independent transmitters on different tanks. You can set alarms for maximum depth and a range of minimum tank pressures.
The remaining dive-time alarm is based on worst-case tank pressure, various degrees of tissue-loading in no-stop scenarios, turn-round tank-pressure (when it’s time to head back), and even elapsed dive-time. The run-timer in Gauge mode counts down in minutes and seconds.
The Atom can give you far too many messages to list here. A summary in the manual would help but it’s an exhausting 150-page read, with no short-cuts.

Oceanic OC1 £850
(£630 without transmitter)

Integrates with multiple tanks.

The OC1 is a nitrox-enabled computer-watch that can be wirelessly integrated with up to
three gas supplies according to the number of transmitters employed – and this can include your buddy’s main tank. Everything is contained within a smart titanium case that’s fine for wearing day to day and is rated to 200m deep.
When using more than one gas, it’s simple to press the Mode button for more than two seconds to enter the gas-switching menu.
Press Advance to scroll to an alternative gas, and Select to choose it. Press Select again to confirm your action.
The digital compass must first be calibrated to your global position. It includes declination for a known longitude and is more complicated than that of some similarly equipped computers. One push-button acknowledges those otherwise annoying audible alarms, and deactivates the current one.
The OC1 has a user-changeable lithium battery, though it is recommended to have the watch pressure-tested after such a change. A limited all-black edition is available.

Oceanic OCS £445

Up to three nitrox mixes per dive.

Available in black composite with either shiny stainless steel or black anodised trim, the OCS
is a simplified OC1 in that it gives no option to wirelessly integrate tank pressure.
It has the same choice of algorithms, a digital compass and can be programmed for up to three nitrox mixes per dive. An optional PC Interface Kit means that you can install operational improvements or even future new features.

Oceanic Geo2 £304

Up to two nitrox mixes per dive.

The entry-level model, rated to 100m, can be programmed for two nitrox mixes and switching is unrestricted in that Gas 1 may have a higher O2 percentage than Gas 2. Stop times of less than three minutes are displayed in minutes and seconds, and there is an option to use a deep-stop function with a countdown timer at half the depth of a dive deeper than 25m.
You can get a PC Interface with OceanLog download and settings upload, and an auto-update to install operational improvements.

TABATA USA IS BASED in Japan but makes most of its products in Taiwan. It’s an important brand worldwide but isn’t too proud to put its name on products made by other diving equipment manufacturers.

Tusa Zen £248

Up to two nitrox mixes per dive.

The algorithm is based on Buhlmann ZHL-16c – the same as the Pelagic Z+ developed by Oceanic for European divers. It’s a development of the ZH-L16 used by numerous independent manufacturers and has a good safety record.
The Zen can be set to default to a worst-case scenario 79% nitrogen, 50% oxygen, but this
will also set the alarms going if you pass 18m without setting the actual nitrox mix you’re using. You can turn this feature off.
The Zen can be set with the right nitrox mix, a second mix, no-default O2 50% setting, audible alarms on or off, a depth alarm, an elapsed time alarm, a dive-time-remaining alarm, PO2 setting, wet activation, deep stop on or off, safety stop on or off, 15sec sampling rate and a conservative factor. Mixes must be set in ascending order.
It’s not easy to tell whether you’re using the computer with gas 1 or 2, as this is shown only by the position of a little tank icon, but other figures displayed are surprisingly legible.
The ascent-rate indicator also builds up during an ascent. The Zen uses one of two ascent rates, according to current depth.
The deep stop seemed to make no difference to the no-stop time displayed, and there is no protest should you decide to ignore it. It was set to come on automatically on any dive deeper than 20m. Go deeper than the chosen pO2 setting for the nitrox mix in use and an alarm sounds, but in Decompression mode this is triggered only if 1.6 bar is exceeded.
Change gas mixes on a dive by pressing one of the four buttons for the right amount of time. You can change to a mix at a depth exceeding its maximum operating depth (MOD) if the tank with the first gas is depleted, but it sounds an alarm and displays “Do Not Change Gas”. You can switch the alarm off when at a safer depth.
The conservative factor, if applied, merely moves the pegging of the algorithm up another 915m of altitude.

LONG AGO, MARES DABBLED with brand-engineering. These days it builds its own computers in Italy, and as such it has taken a slightly different approach to other makers.

Mares Matrix £420

Analogue time & compass displays.
Three nitrox mixes.

What makes this smart full-featured product unique is its use of a rechargeable lithium-ion battery and analogue display for both Time and Compass modes. This display is formed up on the dot matrix LCD and is very easy to read.
The Matrix is intuitive to set up once you appreciate that it is unlike other mainstream computers. It can be set for up to three nitrox mixes (in ascending order of O2 percentages) per dive and uses a 10-tissue RGBM algorithm written for Mares by Bruce Wienke. During a dive, it displays a summary of all and any deco-stops required at the press of a button.
Mounting into a special dock that has a USB2 connection for either a computer or a mains converter plug charges the Matrix, so you don’t have to worry about a battery going flat on a trip. On the other hand, you need to remember to recharge it, preferably every night.
A clear display reveals the state of charge. On a dive, pressing a button will display an up-to-the-moment profile. Deep stops of one or two minutes can be chosen but are not mandatory. A three-minute safety stop is always displayed towards the end of the ascent.

A JAPANESE-MADE computer-watch bore the Scubapro name for a while but only in certain territories. Now the giant conglomerate has produced its own very tough-looking bit of kit.

Scubapro Meridian £399

Up to two nitrox mixes per dive.
Heart-rate integration option.

Like the Galileo or Aladin Tech 2G full-size computers, the Scubapro Meridian uses a modified Buhlmann ZH-8L predictive multi-gas algorithm. You can set one of five micro-bubble levels (MbL1-5) that come into play during repeat dives, or switch that function off altogether (MbL0), so that the unit performs like an old-fashioned Aladin Pro.
The 316 stainless-steel Meridian’s four big buttons stand up loud and proud, with a good throw and strong return springs.
Setting up is easy. You can set a nitrox mix for Gas One from 21-100% O2, with a PO2 maximum from 1.45 to 1.6 bar (or even turn that latter function off).
You can also set a separate deco gas in the same way, with the same range of mixes and a PO2 range of 1.0 to 1.6 bar.
For gas-switching during an ascent, you push the mode button for a second or so and confirm with a second push.
Maximum depth and dive-time alarms can be preset. You can set the 5m safety stop from 0 to 5 minutes. When it asks for a level stop to reduce micro-bubble level risks you can choose to miss it, and it simply reverts to the next less-cautious setting.
PDIS is Scubapro’s own version of deep stops, and you can ask the Meridian to calculate a unique PDIS for every dive, or turn it off.
The ascent rate is monitored and displayed as a percentage of the suggested maximum at that particular depth. The Meridian tells you when to make a safety stop, and counts out the time in both minutes and seconds.
The Meridian can, like the Galileo, be used with a heart-rate monitor. It uses a predictive aspect that takes your heart-rate and thereby any over-exertion that you might experience into account.
The LogTRAK software is compatible with Windows or Mac.