Elapsed Time Bezels On Dive Watches...

[cortopar]

I see misconceptions about this all the time, and so thought this might be of general interest to people.

95% of the reviews and descriptions you read of dive watch (or more properly "elapsed time") bezels will tell you that divers use these so they don't "run out of air." This is totally bogus. Divers keep from running out of air by checking the pressure gauges attached to their air tanks.

Elapsed time bezels are used to track the amount of time you're underwater. When you're down, you're breathing air that is at greater pressure than when you're breathing at the surface. The pressure forces nitrogen into your bloodstream. If you have too much nitrogen in your bloodstream when you surface, the reduction in pressure will cause nitrogen bubbles to form in your blood (the "bends" or decompression sickness).

To avoid DCS, in the "old days" divers used tables that told you how long you could stay underwater at a given depth without having to incorporate decompression stops during your ascent. The whole point of "recreational" or "non-decompression" diving is that in an emergency, you can immediately surface without excessive risk of DCS.

The use of dive tables can result in drastically shortening your "down time" since to be safe, you have to calculate the nitrogen level in your system based on the deepest depth you were at. Modern dive computers are more accurate at taking into account the various depths you experience during a dive and the amount of time spent at each. They don't "penalize" you for your whole dive time if you were say, at 120 feet for only a minute and spent the rest of your dive at 65 feet.

Long-winded way of saying, elapsed time bezels track how long you're underwater for dive table calculations, not to track your air usage.

Hope this was informative.

Best,

Bob

[NaviChief]

Great info! One more way to undress a salesperson at a AD when they slap the "so you don't run out of air" line on you. Just kidding, be kind to everyone, its the holidays.