Explaining the Basics, Debunking the Myths

Timekeeping: The Dive Watch, Deconstructed

July 20, 2011 Design By Photo by Gishani
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It is ironic that, while watch companies are turning out more capable dive watches – helium release valves, absurd water resistance, innovative bezels – fewer and fewer SCUBA divers are wearing watches at all. Go on any dive boat and you’re lucky to find one person wearing anything besides a dive computer on his wrist. The fact of the matter is, dive watches have become anachronistic novelties to all but a few old school divers who still rely on memory and math skills to calculate no-decompression limits. But dive watches are more popular than ever for even those who will never dip a toe in the ocean. Perhaps because of this surge in their popularity, combined with their lack of real world use, dive watches suffer from numerous misconceptions. People love to wear them but don’t know a helium release valve from a no-deco limit. We’re here to help. This article explains some of the basics of the dive watch, debunks some myths and sets things straight.

How Is a Dive Watch Used?

Even if you never plan to back roll into the Caribbean or explore a Great Lakes wreck, you should know how a diver uses a dive watch. For a diver, there are three primary pieces of data he needs to know at all times: his depth, his remaining air pressure and his bottom time. While all three can now be displayed on a modern digital dive computer, the traditional means is using gauges and a timepiece, the first two on analog “brass and glass” gauges attached to a regulator hose or strapped to a wrist and the latter via the dive watch. While the importance of remaining air pressure is easy to understand, depth and time are more theoretical and inextricably linked.

The deeper you dive, the more nitrogen from the compressed air you breathe is absorbed in your body tissue. As you ascend this nitrogen is released slowly but if you spend too long too deep, you have to stop on your way to the surface in order to decompress. Fail to decompress, or ascend too quickly and you risk getting the bends, which can be painful and even deadly. Scientists long ago devised tables that tell divers what the maximum times they can spend at each depth before they must decompress on their ascent. So knowing your depth and your time is vital.

In the early days of diving, the way to track dive time was to pull out the crown of your watch before descending, set the minute hand to twelve o’clock, push in the crown and then start the dive. Of course, this was clumsy and always meant having to reset the time once back on the boat. The introduction of the rotating elapsed time bezel was a big leap forward. Contrary to some misconceptions, the bezel does not track the amount of air in the SCUBA tank. The bezel allows a diver to twist the bezel so that the arrow, or descent marker, aligns with the minute hand. As time passes, the minute hand is read against the bezel markings to quickly tell elapsed dive time. Knowing his depth and this time, along with the no-deco limit for his depth, a diver can safely carry out his dive.

Continues on the next page.

Jason Heaton

Only wears mechanical watches, drives an adequately patina’d Alfa Romeo Spider right up until the snow flies, and always keeps an open bottle of single malt close at hand.

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