Every watch has a bezel. Some bezels just hold the crystal in place, while others have extra functions, too.
Definition and Purpose
A watch bezel is the outermost top ring that surrounds the face of the watch. The bezel can be screwed or snapped on; some are fixed while others can be rotated by hand.
A watch bezel's purpose is simple: It holds the crystal, or glass, watch face in place and protects the watch from damage and malfunctioning. In the 1950s, watchmakers realized that an external bezel was the best way to add functions to a watch without complicating the movement, and so the external watch bezel was born.
Many Uses for a Bezel
Watch bezel functions can be used to monitor diving, timing, speed or distance, as a compass, or to determine heart rate. For example, a diving watch bezel helps divers tell how long they've been under water: A rotating bezel might only move counterclockwise to ensure the diver's safety. A timing bezel might rotate both counterclockwise and clockwise to keep time for parking meters, cakes in the oven or anything the wearer might want to time. The tachymeter bezel is fixed on chronographs; it's used to calculate units per hour, most commonly speed. The pulsometer is also a fixed bezel and has been in use since the 1940s on "doctors' watches." It's used to read a patient's pulse. The bezel can also be purely decorative, with diamonds, expensive metals, contrasting colors or engravings.