How To Use Watch Bezels
Watch bezels - most sports watches have them and a huge variety of dress watches have them...why? Because they are cool. Are they necessary nowadays? Not at all.
With modern technology most functions bezels served were replaced with modern technology, however a bezel can completely make a watch and provide a nice reminder of how divers, pilots and racing drivers once relied on these basic tools. It's all very well owning a nice sports watch but if you don't actually know how to use it, you may end up looking a little silly
The Divers Bezel.
This is arguably the simplest to use. You have a monodirectional clicking bezel with a lume filled plot at 12. You turn the bezel anticlockwise until the 12 lume plot is in line with the minute hand. You can then ignore the dial and use just the minute hand and bezel to time your dive up to an hour.
These are monodirectional so if the bezel was knocked it could only go anticlockwise therefore shortening you dive time. If it was knocked clockwise it would bring the 12 marker closer to the minute hand and potentially cause you to stay under too long.
The GMT Bezel
This is a clever design made originally for pilots so they could keep track of the time as they travelled across time zones. The dial on these watches allows 2 time zones to be shown through the use of 2 independently set hour hands. After setting the 2 hour hands to your departure and destination times you can then move the 24 hour bezel back or forward so that the correct time is level with your GMT hand. This therefore means the main hour hand shows your current time while the GMT hands shows an extra 2 time zones. Many versions of these bezels have the first 12 hours in one colour and the second in a different colour. This shows AM and PM.
The Tachymetre Scale Bezel
This is essentially a small conversion chart so you can take a set distance and measure speed per hour.
The number given on the bezel represents how many units of distance you would have travelled over an hour. The unit of distance is not important so it cold be km, miles, yards etc.
You do however need to know the distance you are traveling. for example if you travelled 1km in 30 seconds the tachymeter would show 120.
This is because if you travelled 1km in 30 seconds you would have travelled 120km per hour.
There are 3600 seconds in a hour. 3600 / 30 is 120.
Telemeter Scale Bezel
This is a less common bezel and actually references distance through the speed of sound. The idea is that you measure the time between seeing an event and hearing it. for example a bomb exploding in the distance. Sound travels at 1234km/s which converts to 20.6 km/m. Therefore the telemeter scale goes from 0-20. This means if an event happens and you start you chronograph hand. 20km per minute. If a bomb explodes and takes 30 seconds for you to hear it, you know it must be approximately 10km away.
There are other types of bezels most of which also work on the principle of converting measuremtns into units/hour along a scale.