In this article in our series on the basics of divers’ watches, we take on what is probably the most distinctive element of a dive watch: the rotating bezel.
Its function is actually quite simple: before a diver’s descent, the 12 o?clock bezel marker is aligned with the minute hand, allowing the elapsed time, up to 60 minutes, to be read on the bezel (which is why quite a few dive watches come with a particularly prominent minute hand). A unidirectional, ratcheting construction ensures that – if the bezel is accidentally moved – the time already spent underwater would be indicated as longer than actually spent, providing the diver with a safety reserve for his now more imminent ascent. The bezel/minute hand combination does not, however, directly measure how much air remains in the air tank, as still can be read quite often in press releases. A standard scuba dive (in which the diver is equipped with a standard air tank) usually lasts 30 to 50 minutes, mostly depending on the depth reached and the shape the diver is in (basically, how physically demanding the dive is). This explains why the first 15 to 20 minutes on the bezel inlay are often more highlighted – the end of this sector theoretically indicates the point of return (exception: “countdown” bezels that mark the time of ascent). In order to correctly time decompression stops at the end of a dive, central-minutes chronographs such as the Aquastar Benthos or even split-minute...