All watches have bezels—the top ring that surrounds the crystal. Some snap on, some screw on, and some can be turned by hand. In the 1950's, watch companies found that the bezel was the perfect place to add functions without adding complications to the movement. Here's a roundup of the more common bezels and how they’re used.
Perhaps the simplest type of bezel tracks elapsed time. It's most commonly associated with dive watches since this is where it found its origins—the Rolex Submariner and Blancpain Fifty Fathoms of the early '50s introduced them. In the days before digital dive computers, a diver would track their time underwater by setting the zero marker (typically a luminous arrow) to line up with the minute hand. As the dive progressed, the elapsed time could be read easily on the outer ring, up to one hour. Most dive bezels now ratchet in half- or one-minute increments and move counterclockwise only. This is so that if the bezel is accidentally bumped, it will only shorten the dive, so the diver won’t think he can stay longer than he should and risk decompression sickness.
Similar to the elapsed time bezel is the countdown time bezel. Instead of time increments going from zero to 60 minutes, they go from 60 minutes to zero. This can be useful for pilots or military or police operations where synchronization is key and knowing when it’s time to go is critical. Set the desired time to match the minute hand and when it reaches zero, you’d better be on the move.
SECOND (OR THIRD) TIME ZONE
The so-called “GMT” bezel is so-named because this style is used to track a second time zone, traditionally Greenwich Mean Time. In the 1950s, jet travel was becoming more common, and Pan Am Airlines asked Rolex to build them a watch for its transatlantic pilots—one that could track both local time and GMT. The resulting watch, the GMT-Master, was the result. Although the standard hour hand was used for local time, an additional 24-hour hand lined up with the hour indicated on the rotating bezel, which could be turned to set the appropriate second time zone.
Most people don’t realize that their analog watch can be used as a compass. If you’re in the Northern Hemisphere, just aim the hour hand in the direction of the sun and South is at a point halfway between the hour hand and 12:00. If your watch has a rotating compass bezel, set the South marker to this point and you can now navigate, remembering to re-check your bearing regularly.
One of the most common fixed bezel is the tachymeter bezel found on chronographs, which saw their debut on the motor-racing watches of the 1960s and '70s. A tachymeter is used to calculate units per hour, most commonly speed. To use, you simply start the chronograph when a car crosses a set mark, such as the starting line, and then stop the chronograph when the car crosses your desired end mark. The units per hour (such as kilometers or miles) are then read on the bezel marking opposite the chronograph’s sweep seconds hand. Though a tachymeter is most commonly associated with speed calculation, it can be used to track any unit, provided it happens in one minute or less.
A telemeter also makes use of a chronograph’s sweep seconds hand but instead of speed, it calculates distance. Originally developed for soldiers to discern the distance of enemy artillery fire, a more peaceful use is to track how far away lightning is during a thunderstorm. Start the chronograph when you see the flash of light, then stop it when you hear the clap of thunder. The distance, typically in kilometers or miles, is shown on the bezel marking opposite the stopped chronograph hand.
The third common fixed bezel found on chronographs is the pulsometer, found on doctors’ watches as far back as the 1940s. Again using the chronograph’s sweep seconds hand, a patient’s pulse can be quickly told without a lot of counting or math. The scale on the bezel will be calibrated to a specific number, such as 15 or 20 beats. Start the chronograph when you detect a pulse at a person’s wrist, then stop it when you’ve counted to that calibration number. The beats per minute will be indicated on the scale opposite the stopped hand.
Perhaps the smartest bezel of all is the slide rule. This one doesn’t use the watch hands at all but merely two logarithmic scales, one stationary and one rotating, that can be used to perform any number of mathematical calculations. Breitling first started using the slide rule bezel in the 1950's on its Navitimer, which soon became standard equipment for pilots who needed quick reference to calculate air speed, fuel consumption, and distances. To use the slide rule bezel, locate the conversion factor number, usually 10, indicated in red on the scale. Then you simply line that up with one of the numbers you want to multiply from the rotating bezel, then find your other multiplier and find your answer opposite it, again on the outer scale.
Source: "How to Read a Watch Bezel." Men's Health. Men's Health, 18 Dec. 2014. Web. 4 July 2016.