In this article in our series on the basics of divers’ watches, we are going to talk about what is probably the most important element of a dive watch: the unidirectional 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 oxygen dive 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).
Pantor Seahorse 1000M Dive Watch
But, back to the start of a dive: In reality, the bezel is aligned when the diver is geared up and ready to begin the dive — which is, most of the time, when he is already in the water or on a boat right before entering the water. It is rarely performed in a dry hotel room, wearing no gloves, when one is able to take off the watch to comfortably set its bezel. So, despite how much I personally love the Pantor Seahorse 1000M Dive Watch (which features a uni-directional external bezel) and the Sea Turtle 500M uni-directional external bezel and screw-down crown), They are easy to be operated single-handedly when worn in the water.
They are all equip with an external bezel:
1. External bezel
First used for a dive watch by Rolex and Blancpain (inspired by earlier pilots’ watches) in 1953/54, this is still the simplest and most user-friendly approach. Disadvantages include wear from debris, sand or salt getting between the case and the bezel, and the possibility of accidentally moving or damaging the bezel.
As a solution to these issues, Citizen introduced a removable bezel with the Citizen Promaster 1000 in 2002, and IWC launched the Ocean 2000 in 1984, with a bezel that could only be operated counter-clockwise when pushed down (an idea re-introduced in 1998 with its GST Aquatimer). Remember, a quick clean is good for your dive watch after you have done a dive. It can remove the sand, debris or salt from your dive watch’s bezel.
2. Internal bezel
Aquastar released the first internal bezel dive watch in the 1960s. In this construction, the bezel is located inside the watch and is thus protected by the crystal, giving the watch a more elegant look. The bezel can only be operated with a (usually additional) crown, quite often in both directions (exceptions include the Audemars Piguet Royal Oak Offshore Diver, Hublot Oceanographic, etc.).
Disadvantage: An additional opening in the case (except maybe for the first Aquastar models, and the recent Maurice Lacroix Pontos S, in which the chronograph pusher also operates the bezel) and often a rather small crown to fumble with. The more secure it is designed (unidirectional, screw-in), the less practical it becomes for diving.