Bezel is the term used to describe the rim that fastens the watch crystal to the case. Bezels can be decorative or serve a specific function.
Elapsed Time
Rolex Submariner
Elapsed Time Bezel is a unidirectional, rotating bezel that is used to calculate the amount of time that has passed. This bezel can usually be found of diving watches such as Rolex Submariner, Rolex Sea Dweller, and Rolex Deep Sea Dweller.
Tachymeter
Rolex Daytona with Tachymeter Bezel
A tachymeter bezel is used to calculate speed based on travel time or to measure distance based on speed. The tachymeter functions independently of the unit of distance as long as the unit is consistent throughout all measurement and calculation. A tachymeter can also be used to measure industrial production in units per hour. Simply put, a tachymeter is a way to convert elapsed time in seconds per unit to units per hour.
Slide-Rule
Breitling Navitimer with a Slide-Rule Bezel
A Slide-rule Bezel is used to perform complex calculations without the use of a calculator. Slide-rule is especially useful for navigation when no other devises are available. To perform calculations, the rings of the bezel are rotated in appropriate corresponding positions allowing the wearer to read the result.
24 Hour
Rolex GMT-Master with a 24 Hour Bezel
24 Hour Bezel is a way to keep track of time in two different time zones. Once set, the bezel will complete a full revolution once every 24 hours. Rolex GMT was the first watch to be mass produced with the 24 hour function upon request from PanAm.
Decorative
Decorative bezels are designed to captivate and stimulate the senses of the viewer. A decorative bezel can be as complex and intriguing or as simple and streamlined as the designer envisioned it. Decorative bezels are often set with diamonds or have engraved patterns.
Cerachrom
Cerachrom bezel was designed by Rolex for their new line of GMT-Master II watches. Cerachrom is a high temperature process in which the dual color ceramic component of the bezel is produced as a single piece.