Before splashing out on a dive computer, it’s a good idea to take stock of your current diving profile and review and analyse what form your diving is likely to take in the coming years.
Even without recourse to a crystal ball, it’s easy to know where your interests lie and how your diving is likely to develop, and this will go a long way to helping you make the best choice.
Ask yourself a few questions: are you likely to progress to nitrox use, engage in decompression, try gas switching, trimix or rebreather diving?
Do you require air integration to monitor gas use and remaining dive time? Do you prefer wrist or console-mounted units? Is the ability to download your dive profile to a Mac or PC important to you?
Thinking ahead and choosing a computer that possibly has more features than you may initially require will offer the chance for the device to grow alongside your diving experience while also making a considerable financial saving in the long term.
Displays should be clear, concise and uncluttered, with the most important information of depth and remaining bottom time easily identifiable.
If you’re a spectacles wearer, make sure the display is large enough to read and also consider how screen technology can be of benefit. With most computer screens featuring a black on grey display, a selectable backlight for night diving and low-light conditions is of obvious advantage, or perhaps one of the colourful new generation OLED displays may fit the bill.
Console or wrist?
This is entirely a matter of personal choice, although both console-mounted (above) and wrist computers do benefit from larger, clearer displays than their smaller watch-sized counterparts.
Audible alarms can be a useful tool and can be programmed to give many different alerts, including maximum depth, dive time and ascent rate, leaving you free to concentrate on enjoying the dive and not a slave to your computer screen.
User-changeable batteries are an obvious advantage, while the option to download your dives to a PC can allow step-by-step analysis of your profile in graph format, allow your history to be stored in digital format or printed out in the form of a traditional logbook.
Many computers also have the benefit of an electronic compass to aid navigation and some feature upgradeable software options to allow more advanced diving to be undertaken if and when required.
Changing the settings on your computer menu should be easy and intuitive at the surface and below it. If you’re continually referring to your user manual then your computer is possibly too complicated for your immediate needs.
While a basic air-only computer will calculate your dives at 21 per cent oxygen, a nitrox version will also do the same and many manufacturers’ entry-level computers feature up to a 40 per cent nitrox mix, suitable for recreational use.
Above 40 per cent and a more advanced computer is required, which may also incorporate the ability to switch between gases during your dive as an aid to decompression.
At the other end of the scale, trimix and CCR computers allow multiple switches to be made for those carrying out deeper and more complicated diving profiles.
There are two types of air-integrated computer – those that measure tank pressure via a high-pressure hose connection to replace the traditional analogue gauge, and wireless versions where information is transmitted via a sensor direct to your computer.
Both types will estimate the amount of breathing time a diver has left, based on the rate of gas consumed.
An algorithm is simply a theoretical calculation designed to prevent decompression sickness, or DCS, from occurring.
JBS Haldane’s experiments in the early part of the twentieth century determined that different parts of the body absorbed and released nitrogen at different rates.
He showed how the tissues in the human body could be described in time factors or half times – that is how long a tissue takes to accumulate and release nitrogen during a dive. Originally dividing the body into five ‘compartments’, this Haldanean theory still forms the basis for the various decompression models we use to this day
Most deco models work using up to 14 of these fast and slow tissue compartments – imaginary tissues that are designated as fast or slow to describe their rate of saturation – although in effect real tissues may vary in their ability to saturate.
And while all algorithms created for dive computers are obviously created to prevent DCS, being a mathematical calculation means that not all algorithms are the same.
This can result in sometimes widely varying no-stop or decompression times between individuals on the same dive with identical profiles dependent on the make or model of the computer they are using. Most modern dive computers allow you to adjust how liberal or conservative the programmed decompression algorithm is set to.