Timing A Dive Using An Automatic Dive Watch

Timing A Dive Using An Automatic Dive Watch

An automatic dive watch will often feature a rotating bezel, that allows for an easier reading of elapsed time of under one hour from a specific point. This is used to compute the length of a dive. When the zero on the bezel is aligned with the watch's seconds or minutes hand on the water entry moment a diver can read off the elapsed time from the bezel. This saves the diver having to remember the exact water entry moment and having to perform arithmetic’s that would be necessary if the watch's regular dial was used. On an automatic dive watch the bezel is "unidirectional", i.e., it contains a ratchet so it can only be turned anti-clockwise to increase the apparent elapsed time. This is an important fail safe feature. If the bezel could be turned clockwise this could suggest to a diver that the elapsed time was shorter than reality, thus indicating a falsely short elapsed time reading and therefore falsely low air consumption assumptions which are highly dangerous. Some diving watch models feature a lockable bezel to minimize the chance of unintentional bezel operation under water.

The exclusive use of a rotating bezel is considered a rudimentary diving technique in the 21^th century, suitable for basic shallow single gas (air) diving only. Non-basic diving profiles and depths past 30 m (98 ft) require other more advanced timing and measuring methods to establish suitable decompression profiles to avoid decompression sickness. Besides for basic diving and as a backup for more complex diving, the one-way bezel can also be used for other situations in which a measurement of elapsed time of under one hour might be useful.

Digital dive watches usually perform the elapsed timer function by use of a standard stop watch function. Digital dive watches may also feature a depth gauge and logging features, but are not usually regarded as a substitute for a dedicated dive computer.