I think it's safe to say that nowadays dive tables are the reserve of those first few dives while in training, or maybe for the diver who only does a couple of resort dives a year. Once qualified or indeed during qualification, the majority of divers use computers. It stands to reason, computers take the hard work out of finding the correct bottom time, and reduce the potential for making mistakes, especially on repetitive dives. Their greatest asset is that they can recalculate your decompression obligation every few seconds, and as a consequence can increase your dive time depending upon the situation.
We picked seven of the most popular computers that retail for under £250 (one is just over £250), and took them for a couple of days' diving off Land's End to find out. All of them performed remarkably well. We checked their settings before taking them into open water, but all of them could have been used straight out of the box. It was also good to report that, without exception, they had all been set to metric rather than imperial measurements. The main differences between the models are their algorithms. Some allow longer dives or are less conservative, depending on how you view things. Some cram as much information onto the display as possible, while others require you to push a button and activate a second display. All models have user-replaceable batteries and the majority come with screen protectors.
One factor let all of the computers down to some extent and that was the instruction manuals. In some cases they were just plain wrong, referring to diagrams that were labelled differently or not labelled at all! Some were so confusing we resorted to trial and error to find out how they worked. A few manufacturers claim in their literature that their units shouldn't be used for any form of decompression diving. They go on to say that they display decompression information purely in case you accidentally go over your no-stop time. What, for tens of minutes?
Other manuals warn you not to dive below 40m, yet display a depth of up to 150m. These are there purely as 'Get out of jail' clauses - it's the world of litigation in which we now live!
Please find all the computer tests detailed below:
