Features & Use of the One-Way Rotating Bezel
As with many things these days the functions provided by a unidirectional bezel can be provided by computer but what happens when that computer fails? Much of diving safe is about redundancy and components like watches, depth and pressure gauges provide that edge.
It allows dive time to be tracked in a way that is fairly failsafe. Along with depth, proper breathing, rate of ascent, etc., divers must know how long they’re been down otherwise they risk serious injury or even death due to Decompression Illness (DCI).
Basically a rotating bezel is a simple device found on most any decent quality dive watch except for those providing the same feature electronically by computer, instead of by mechanical means. It can also be found on watches not specifically made for diving, where it usually serves only as an event timer, and not so much as a safety device.
The bezel itself is the large ring that encircles the crystal covering the watch face. It usually has numerals at ten minute increments with tic marks in-between. Also there is a pointer mark at the zero position to indicate a starting point.
Depending on your dive profile there are several ways to use it but most often it’s used to time the entire dive. You align the bezel pointer with the minute hand at the start of your dive, and can tell at a glance how much time is left before having to ascend. The safety feature of the bezel lies in its being unidirectional or one-way.
Also important is it can only be turned counter-clockwise – opposite the direction the hands are moving. That means if the bezel gets bumped hard enough to rotate, it will show a longer elapsed time, causing the diver to automatically err on the side of caution. It’s obviously better to believe their time is up and ascend early rather than stay down too long thinking there is plenty of time left.
A good elapsed time bezel will be easy to read, and fit snug enough so as to require a slight effort to turn it. There should be internal indents which cause the bezel to ratchet as it’s turned and allow it to “catch”, aligning the pointer to precisely wherever the minute hand is pointing. Again, it must only rotate counterclockwise, and have knurled or notched edges making it easy to grasp even with gloves on underwater.
Many divers, particularly those who got certified before the advent of dive computers or at least before they became mainstream, understand the purpose of a rotating bezel, but for those who don’t or who are getting a dive watch for someone else, hopefully this has provided some illumination.
For myself, even though having dived for years with a computer, I still find a level of comfort in using a dive watch and setting the bezel at the start of every dive. Its simplicity and time-tested mechanical reliability make a great backup for electronics.
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