I LIKE BEING UNDER WATER so much that I’ve devoted the past 20 years of my life to it.
I suppose I’m more of an underwater photographer than a pure diver. I know that many of you love the technical aspects of diving, but I just use those aspects to get where I need to go.
If it’s a dive for which a single tank on nitrox is appropriate, I’ll use that. If it’s a dive that requires multiple gases in multiple tanks, so be it. If it requires a closed-circuit rebreather, I’ll use that. However, I choose the tools to suit the job, rather than choosing the tools before looking for the circumstances in which to use them.
This may sound strange coming from someone who has spent two decades writing about diving equipment, but I’m not that obsessed by the techniques. I’d love all my dives to be in less than 10m of water with lots of big animals, no currents and spectacular shipwrecks, but then that’s just dreaming.
This said, it comes as no surprise that I once made three trips to long-haul destinations with the same very well-known technical diving computer before I managed to fathom out how to use it successfully.
I’m always daunted when some hopeful importer sends me another technical diving computer, because I know it’s going to strain my brain.
Not so the Dive System Orca.

Computer & Algorithm
Dive System is a small company in Italy that makes its entire range of diving equipment in-house.
As such, I’m told that it tests everything it makes multiple times to achieve 100% reliability.
The Orca computer is subject to this same testing. I got it out of its box and, by means of its two buttons, set it up to go diving. It was so easy that even I could use it.
The display is not at all sexy. Its LCD is one colour (black) on a typically neutral green/grey background that is illuminated by a backlight if needs be.
Unusually, it employs a choice of two algorithms; one a Buhlmann derivative (ZHL-16B) such as you will find in most mainstream diving computers, the other VPM B, now popular with many technical divers.
If you are like me and feel unsure as to which is more suitable for the diving you plan to do, you can also choose to run the Orca with the algorithm using VPM-B as the main mode, while the Buhlmann ZHL-16B runs in the background, keeping you away from the edge of disaster once you get up into the shallows.
The Buhlmann algorithm allows you to adjust the gradient factors, but before you embark on this inherently risky option, I suggest that you read all you can on the subject.
The Orca also uses an adaptive “sigmoidal” model to optimise decompression calculations for repetitive dives. A sigmoid curve is produced by a mathematical function having an “S” shape (I read that online!). It really takes effect only with surface intervals of less than two hours.
This diving computer allows a degree of personal adjustment that goes a lot further than mainstream models. It allows you to choose three depth zones in which you might prefer to do mandated deco-stops.
It can be preset for use with nitrox and helium mixes with up to a dozen open-circuit mixes configurable, and it can operate to a maximum single dive time of around 33 hours and 20 minutes. That’s enough for me.
Its connection for downloading to a PC is by Bluetooth.
The Orca is set up and operated by means of two positive buttons. The right one moves the menu on, while the left confirms what you have chosen.

In the Water
The main screen indicates your current depth and dive duration, the algorithm you are using and the mix you have set to breathe. In NDL mode it shows the remaining no-deco-stop dive time.
Pressing the right (Confirm or Commit) button brings up the second main screen with your maximum PO2, CNS, OUT and maximum depth achieved during that dive.
Pressing that button again brings up the third main screen, which adds the average depth, the activated mix in open-circuit (or selected diluent if used in CCR mode), battery voltage and water temperature.
You can preset mixes either as enabled or disabled. This allows you to conveniently store mixes that you may not actually be using on a particular dive. You can activate only one gas setting at any one time, and this should be the one you are breathing.
The total time to surface is calculated based on all the gases that have been enabled and it is presumed that you will be breathing the appropriate one.
Once the Orca gets into mandatory decompression, it displays stop times and stop depths. It’s all very straightforward. If you have enabled several gases, it will suggest the best one, which you can activate and commit to by operating the two buttons.
For simple no-deco-stop diving, a 5m safety stop can be enabled. If you have bought this computer with an eye to the future rather than for the diving you are doing at present, you can choose to use it with a basic menu instead of the advanced one.
It can also be used in Gauge mode. Then it displays depth and time but it also has a timer with minutes and seconds function.
The computer cannot be turned off while diving but it’s an option (to preserve battery life) after 10 minutes from surfacing. It continues to update tissue status, however.
It can display a simple depth/time profile of your dive at this time.
What I mainly liked about this computer was that I could pick it up and use it without too much ado. It may not provide any computer games for long hangs, but that’s what paperback books are for!
The Orca is a chunky bit of kit and takes up quite a bit of space on your arm. Its display is a little over-functional (there are sexier-looking options available) and the anodising soon picked up a few scratches, but it does everything you need as a multi-gas diver.

Liquivision Xeo, £736
Shearwater Petrel, £730
VR Technology VRX OLED, from £945

PRICE £720
BATTERY 3V CR123 Trustfire lithium (user-replaceable)
FIRMWARE Updatable
LOGBOOK 100 hours
CONTACT www.manfrog.co.uk
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