When you own a complicated watch that features different scales and functions around the bezel, knowing what they are and how they work is essential. Sure, not everyone wearing these watches are going to be using the functions in daily life but you should at least know how to use it and what it’s for (if for nothing more than showing it off).
Most Common Bezel Functions
Bezels have been designed to time races, count down to the start of races, take a pulse, calculate remaining fuel or even how to create trajectory adjustments (like the Speedmaster and Apollo 13).
A count up bezel is most commonly found on a dive watch. The scale goes from zero to 60 around the bezel, aligning with the minutes in an hour. Typically, the first 15 to 20 minutes are marked in one minute increments while the rest of the bezel is marked in five minute markers. These bezels are uni-directional counter clockwise to avoid running out of air during a dive. If you accidentally bump the bezel during a dive, you will have less time meaning more air remaining in your tank.
To use a count-up bezel, set the zero marker at the minute hand. As the time passes, you can read off elapsed time on the bezel.
Countdown bezels are similar to a count-up bezel but the minute track is reversed on the bezel; they go from 60 minutes to zero. This is used to set the time remaining before or during an event.
Rotate the bezel so that the time remaining is set to the minute hand; when the minute hand reaches zero on the scale your timer is done.
Outside of dive watches, the tachymeter is a very common scale found on fixed bezels with a chronograph. A tachymeter is used to calculate units per hour; speed is the most common calculation but it can track any unit for timing that can happen in one minute or less.
To use a tachymeter, start the chronograph when a car crosses a set mark, such as the starting line or mile marker, set a desired end mark and stop the chronograph when the car crosses the line. The units per hour are read through the bezel marking lining up with the chronograph seconds hand.
An uncommon scale found on most watches but found on specialized medical watches is a pulsometer. It is designed similar to a tachymeter but rather than tracing units per hour, it determines heart rate. Scales are calibrated from 15 to 30 pulses. The pulsometer dates back to doctors watches from the 1940s.
Start the chronograph timer and count the beats until you get to the number the scale is calibrated for. Stop the time and you will read the heart rate in beats per minute.
Another complication similar to a tachymeter is the telemeter. Rather than calculating speed, this calculates distance for an event that can be seen and heard. The telemeter was originally designed for soldiers to calculate the distance of enemy fire, however today determining the distance of a thunderstorm is much more common.
Start the chronograph when you see the flash and stop when you hear the thunder roar. This will calculate the distance in miles or kilometer on the telemeter scale.
Having a GMT bezel is very helpful in travel as it can track a second time zone and a local time. The standard hour hand would be used for local time with a second 24-hour hand to line up with the hour on the rotating bezel. The bezel would also be marked with a 24-hour scale.
Typically, this 24-hour hand would be set to Greenwich Mean Time as it was the basis for all clocks. Today, you can set the second 24-hour hand to track any timezone.
The slide rule doesn’t require use of the watch hands but is one of the more complicated bezels. Instead of hands, it uses a stationary scale and rotating scale which can be used to perform a number of calculations. This became standard on pilot watches for when they needed quick reference calculating airspeed, fuel consumption and distance.
Locate the conversion factor number, typically 10, indicated in red on the scale. Line this up with one of the numbers you want to multiply from the rotating bezel. Find your other multiplier and find your answer on the outer scale.