The function of a bevel in a dive is quite simple: before the diver descends, the 12-bevel marker must be aligned with the timer, allowing the elapsed time of up to 60 minutes to be read on the bevel.
A unidirectional bezel which has a ratchet ensures that (if the bevelle is moved accidentally) the time already spent underwater would indicate how much time has actually been spent, providing the diver with a more accurate indication towards safety for his ascent now more imminent. However, the bevel / timer combination does not directly measure the amount of air remaining in the air tank, since a standard dive (where the diver is equipped with a standard air tank) usually lasts for 30 to 50 minutes , depending to a great extent on the depth reached and the way the diver is. This explains why the first 15 to 20 minutes of the bevel are more prominent - the end of this bevel theoretically indicates the return point; in order to correctly return to the surface and perform the decompression stops at the end of a dive.
But, back to the beginning of a dive: Actually, the bezel lines up when the diver is ready and ready to begin the dive - which is, most of the time, when he is already in the water or on a boat before enter the water. It is rarely performed in a dry hotel room, without gloves, when one is able to remove the clock to comfortably adjust its bezel.
So we find a great variety of Watches Depthmeters that will facilitate the Immersion since the bezel of the said Clock is the one that will serve as a starting point for this immersion.