Side by Side
The first thing that struck me when comparing all these computers was just how close the decompression information they provided was, regardless of the units I was comparing.
They weren’t identical, but the differences on the first dive of any day were small, regardless of the amount of deco I might have incurred.
That shouldn’t be hugely surprising – seven of the 10 used the Buhlmann ZHL-16 algorithm, with only the Suunto Eon Core, Mares Puck Pro and Quad Air using something different.
Repetitive diving didn’t reveal many differences between the units either. All the computers on test entered mandatory deco at roughly the same time and counted up stops at roughly the same rate, although the Suunto and Mares units stood out.
For example, when I dived the Suunto Eon Core, using Suunto’s own Fused RGBM algorithm, alongside the Scubapro G2, using a Buhlmann algorithm, on two repetitive deco dives on the Rosalie Moller wreck, they were pretty much neck-and-neck on the first dive.
The Suunto asked for a couple of extra minutes of stops, neither here nor there. On the second dive, however, the Suunto gave me a longer no-deco time at depth, but once into mandatory deco the stops it required increased more quickly.
Back at 6m it required significantly longer stops. I’m not suggesting that either was right or wrong, just that they’re different and that you need to know.
What did surprise me was that if I had already completed a couple of dives in the day, then took an undived unit on the third dive, the difference in ascent plans recommended by the previously dived and the undived units wasn’t huge.
The undived unit always allowed me more no-deco time or required shorter mandatory stops, of course, but not by as much as I’d expected.
And the gap between the end of the night dive and the first dive of the next day, usually around 10 hours, pretty much eliminated any differences at all.
Many of the test computers offered gas-switching, from two to 10 gases on a dive. Some were nitrox only, others could be set for trimix. Setting and enabling gases was invariably straightforward, and again familiarity with a specific unit was key.
Without exception the gas-switching process was simple, though the Suunto Eon Core stood out as simplest of all, and all the units could deal with missed switches by recalculating the ascent schedule.
All 10 computers were capable of making a late gas-switch, or of returning to a previously used gas and recalculating the ascent plan.
Deep stops were a common feature, and the units fell into two groups, those basing their deep-stop depth on the maximum dive-depth and those that use the decompression algorithm to calculate a stop depth. Both required some attention on ascent to ensure that I didn’t miss the stop.
I normally make my deep stops at half maximum depth, so found that they fitted me better, though I’m not saying that they were better.
As a rule of thumb, units that calculated the stop depth, like the Mares, called for the deep stop a little shallower than half maximum depth, but that was profile-dependent.
Whether you do your last stop at 6m or 3m makes a big difference to the time you need to stay there to off-gas. Some of the computers display the time required at your actual depth, while others show the time required and the depth at which they think you should be.
The Mares Puck Pro Plus and Quad Air were the obvious examples, their screens displaying the length of the last stop required at 3m, so if you stop deeper and are off-gassing more slowly you’ll need to stay there longer.
It actually feels as if the clock on the unit has slowed to a crawl.
I call these Mares minutes, because I remember them from a Mares M1 RGBM I used to have.
The Suunto Eon Core does this differently and displays the length of stops at your current depth, so moving from 6m to 3m can make a significant difference to the length of stop time displayed.
Your stop time won’t be different, it’s just shown differently, so you need to be aware of how your computer works when calculating your gas requirement.
Finally, all the units offer a Gauge mode, so provided you’re diving within the depth limit of the computer you can plan your dive in advance and then use it as a depth- and dive-timer.
The gas-integrated units allow you to monitor cylinder contents in Gauge mode.
Far more important in real life than all this stop stuff was the clarity of the information provided on the dive, determined by a combination of screen size, amount of data displayed and layout.
The biggest single factor was familiarity with the specific computer. Diving so many computers back to back meant that I needed to recalibrate my head for each one, because they displayed the data in slightly different ways, with more or less additional information available either on the main screen or on one or more alternative screens.
I was still finding new screens on some of the units at the end of the week, which at least gave me something to do on stops, but I preferred those units that gave me essential data and nothing else.
The easiest units to read overall were those that presented only the basic information, such as the Mares Puck Pro Plus or Oceanic Veo 2.0, or which presented the data big and bold and in yer face, like the Suunto Eon Core, Oceanic Pro Plus X and the Ratio iX3M.
The bright, permanently lit colour screen of the Suunto or the illuminated lettering of the Scubapro G2 were easier to read than the similarly sized screen of the Mares Quad Air in low vis and low light, but then I find permanently illuminated computers distracting on night-dives and prefer one that’s dark until required. The TUSA with its automatic backlight was excellent in that respect.
You might have expected the slightly smaller watch-style units to be at a disadvantage on readability, but they were just as intelligible as the bigger computers thanks to careful choice of what to show and where, and in reality the screens weren’t really much smaller.
What it all adds up to, somewhat unexpectedly, perhaps, is that divers picking what they like the look of is an entirely reasonable way to go about choosing a dive-computer, provided the computer you choose does enough to support your own diving.
Used within their limits, any of these computers will deliver excellent service.