Because of the limits imposed by decompression requirements, the diver needs to be able to accurately monitor time and depth throughout the course of the dive. These parameters can either be measured manually through the use of a watch and depth gauge, or electronically by means of a dive timer or diving computer.
A diving watch can be mechanical or electronic and the display can be analogue or digital. The essential requirements are that the watch should be waterproof to at least the maximum depth the diver might expect to dive to and that the watch should be capable of measuring the duration of the dive. The latter can be achieved by means of a stop start mechanism, or a rotating bezel on the outside of the watch casing. Some watches may have both systems and can time the dive and also the surface interval. If the watch has to fit over a wetsuit or drysuit, it is essential that the retaining strap should be sufficiently adjustable to allow for this.
Several types are available, all of which respond to water pressure and are fitted with a display calibrated in metres or feet. Depending on the style of gauge purchased, different sections of the depth scale may be magnified, usually for greater sensitivity at shallower depths. It is important that all gauges have a clear scale with easy to read figures and markings. Divisions for every one metre enable the gauge to be used with any decompression table, but divisions for every three metres will satisfy the BSAC 88 tables.
The function of both watch and depth gauge can be combined into a single instrument. The electronic 'dive timer' is one such example. The dive timer displays simply the depth and dive time throughout the course of the dive. Most dive timers start automatically so there is no danger of forgetting to start them at the begining of the dive. A good dive timer will cost less than a depth gauge and watch combined, so provides a cost effective solution.
With the advent of microelectronics, different types of instruments are possible. The most noticeable of these is the Dive Computer. The Computer combines the function of the watch , the depth gauge and the decompression table. Many different styles are available and all present information in different manners.
The vital information to be displayed underwater includes depth, dive time and current decompression status. On the surface, a computer should display surface interval time and current diving limits.
For a more detailed discussion of the in's and out's of computers read our mirror of the excellent Internet Dive Computer Review (IDCR).
