In this installment in our series on the basics of divers’ watches, we explain why some dive watches have built-in helium-release valves and why others don?t. We also explain why each type is perfectly OK, depending on the type of diving you do.
Comparing ?diving? as most people know it to ?saturation diving? is a bit like comparing an amateur bicyclist to a professional construction worker. They might share the same environment and the same need to breathe, but other than that, they are in fact doing quite different things (this applies to most types of diving, by the way). Saturation diving (meaning the diver?s tissues have absorbed the maximum of gas possible) was practically explored at the end of the 1930s in order to (A.) reduce a diver?s risk of decompression sickness when (B.) working at great depth for (C.) long periods of time ? in other words, to increase both effectiveness and safety. At the end of the 1950s, the necessary scientific basis was provided to begin saturation diving in the military and, soon after, to use it on a commercial basis. In short: such a diver works under water and lives in a dry, pressurized environment for up to several weeks, and is decompressed to surface pressure only once, at the end of the mission.

And this is when some of the earlier, standard dive watches started to show problems ? not with the outside pressure that they were successfully built to withstand but, rather unexpectedly, with pressure from the inside of the watc...