Is it important and should anyone really care? Well, it could be important - all depends on what you're going to do with it. Actually, many folks who may know what it is, don't altogether understand how this simple mechanical device can help avoid serious injury.

I got the question again the other day from a customer on my dive watch site, so decided to get the answer documented for others who may find themselves wondering the same thing.

As with many items, it's fairly intuitive to figure out how to use, and what purpose it may serve, assuming you have one in hand. But if that's not the case and your only interest in a product with this feature is to try and please someone else, then some definitive information would certainly be useful in determining if this very wordy, important sounding feature is actually desirable, or just a bunch of hooey.

To begin with, this is a 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.

To be precise, it is the relatively large, usually metal, ring that encircles the crystal covering the watch face. It generally has the same indicators or tic marks for minutes as the watch, with actual numerals designating each ten minute increment. It also has a pointer mark at the zero position to indicate a starting point.

It's importance lies in an ability to not only aid in tracking dive time, but doing it in a way that is somewhat failsafe. Along with depth, proper breathing, rate of ascent, etc., precise knowledge of how long you've been down is critical to enjoying a safe dive. Getting it wrong can lead to Decompression Illness (DCI) resulting in injury or death.

There are several ways to utilize it for different dive profiles, but most often, it's used to time the whole 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.

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. By believing time is up and ascending earlier, they will avoid being fooled into staying down too long thinking they still had plenty of time left.

On a dive watch, a good rotating 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. Of course it must only rotate counterclockwise, and should also be knurled or notched around the outer edge so it's easy to grasp and turn in water or with gloves.

So now you know. Its usefulness and benefit are inherent in its simplicity, and being purely mechanical, it makes a good backup for anything electronic. In fact, even though having dived for years with a computer, I still utilize a watch with this time-tested device for backup, and set it prior to every dive. Just like in the old days, it continues to add a familiar level of comfort.