Selecting a Dive Computer


It wasn’t too long ago when dive computers were a rare thing to see. Almost all dive planning was done using tables such as the US Navy tables or the DSAT Recreation Dive Planner. Many divers did not trust this large wrist mounted watch that told you how long you could stay down for, and they were right not to fully trust them. They were only to be used alongside with dive tables so that if anything did go wrong the diver could easily spot them.

Nowadays dive computers are seen on the wrist of every dive professional and avid divers alike, I have even taught open water students who have come for their first confined session with their own computer. In fact many divers choose to have a second computer as back up so if one fails they can safely ascend using the second. There are many advantages of using a dive computer, however many divers start to switch off their brain underwater as they believe the computer will always look after them. For this reason it is always a good idea to have a good knowledge of the tables, At least know the NDL (no decompression limit) for a few depths you will be diving, instead of getting down to 30 metres and your computer giving you an NDL of 50 minutes; it is supposed to be 20 minutes!

You will find that different computers can give slightly different readings, such as different NDL’s at certain depths. This is because they use different algorithms. This shouldn’t create too much of a problem as for safety when diving in a group you should always follow to most conservative computer anyway.

All computers have a few features in common, they are all either wrist mounted or gauge mounted, although Oceanic have produced a computer/mask combination which allows you to read your information through a HUD (Heads up display). All computers will read your current depth, maximum depth, current time, dive time and NDL. Most of them also include temperature and a stop watch. They also have built in alarms as warnings for low NDL, ascent rate warning and bottom time/maximum depth.

When selecting a dive computer there are many different features you will need to look, many of them require to be sent to the manufacturer to have the battery changed where some are user changeable. Nowadays all computers come with standard air setting and nitrox settings up to 50%, but if you are thinking about Trimix diving then you can get multi gas computers as well. The market has even opened up to make them into fashionable items with most manufacturers producing wrist watch sized computers so you can wear them when not diving.

Also a nice feature which is becoming more and more popular is air integration. These computers come with a transmitter that you attach to the high pressure port of your regulator 1st stage (although you should still have an SPG for back up) and transmits a signal to your computer not only telling you your current tank pressure, but it also calculates how long your dive will last with your current air consumption. Not a bad feature to have!

When choosing your computer it is always a nice idea to check the features of a few models and not just go for the most basic. For instance you can pick up a Suunto Zoop for around £170 however for an additional £50 you can pick up a Suunto Vyper which allows you to turn off your decompression information turning it into a depth gauge timer, A nice feature if you want to get into mixed gas decompression diving. It is annoying when you have to replace a perfectly good piece of equipment because it isn’t capable of allowing you to progress in your SCUBA career.

Most computers usually come with computer software which is basically a logbook that also keeps track of your dive profile, and allows to track exactly where you were at each second of the dive. Some computers come with the USB cable free of charge, where others you have to buy separately, sometimes costing up to £50!

‘Selecting a Dive Computer’ was written by Mike