What's it for?

[McNoodle]

What is a rotating bezel on a watch for, and how do you 'use' it? My watch has one with markings at 10, 20,30,40 & 50 and rotates anticlockwise.

[fo3nix]

Mostly they're just a fashion accessory, but they can have some uses.

Divers can use them to track how much air they've got left. You set the bezel at the minute hand, and as the minute hand ticks away, you'll see how much time you've got left (you may have 30mins of oxygen with you, for example).

Note that they're unidirectional (only turn one way), so that if a diver hits the watch accidentally on a rock or something and it turns the bezel, it'll err on the side of caution. It'll show less time available, not more -- so they don't die down there thinking they've got plenty of oxygen left.

[Clanad]

Hey! What a great answer, fo3nix... Learn something every day! Are you a diver?

[dundurn]

Clanad - just accepted with thanks your ratatouille recipe! - I use the bezel on my watch when I'm working on different projects simultaneously and want to cost my time reasonably accurately. As I switch to a new task I jot down the elapsed time against the "old" job, reset the bezel and then I can forget about clock-watching until I change projects again.

[Brooksy]

Handy egg timer!

[fo3nix]

Clanad: no, I just thought about the same thing McNoodle did a while back.

[heathfield]

Even if you're not a diver, you can set the bezel to remind yourself how much time you've got till the parking meter runs out! (Or how much flying time you have left before the fuel runs out, huh, Clanad?). lol

[Panic Button]

As a lorry driver I turn the arrow to the minute hand when I start a break. I can then see at a glance how long I have been on a break for.

[jake-the-peg]

I don't think fo3nix is a diver from that answer :c)

I used to teach diving at a University club.

Firstly you don't have oxygen in your tank but (normally) compressed air. Pure Oxygen is actually poisonous below about 10m.

Secondly you'd never time your air supply. People use air at different rates. You have a contents guage that tells you the pressure in your tank. Normally marked red at 50 bar.

You would use a watch to time your time underwater for decompression purposes (so you don't get the bends) although even when I was diving 15 years ago computers were begining to come in for this.

Also stop watch digital functions were popular.

A real divers watch will have a really big chunky bezel so that it can be easily adjusted when youre wearing gloves.

Large clear markings with good glow in the dark properties and a rubber strap although there are some nice metal straps with a fold in link so that they can be used on the outside of a wet or dry suit without adustment.

Oh and being waterproof is a bonus! good rule of thumb is you need a depth rating 3 times how deep you'll be going. As sport diving is pretty much limited to 50m anything claiming much over 200m is a bit pointless.

And yes you just rotate the bezel to the minute hand's position at start and read off your time from the bezel. It only rotates anti-clockwise so that if it gets knocked it can only read longer and not shorter.

A sort of failsafe so that you never think you've got more time than you have.

[fo3nix]

jake: yea, that was the kind of timing I meant. And no, as above, I'm no diver. Thanks for the more detailed answer!

[McNoodle]

Now that makes more sense - reading how long you've been down for. If it were to be used to read how much 'air' you had left, the numbers would be arranged as to decrease as the minute hand rotated.
Thanks all.