What is a rotating bezel?

A rotating bezel is a circular piece around the crystal of a mechanical watch capable of rotating in one direction or both with markings at five minute intervals. A rotating bezel is used to mark the passage of a specific amount of elapsed time under an hour.

Philip Van Horn Weems was granted a patent for a wristwatch with a more functional bezel in 1935. Later, Longines manufactured the Weems watch; it featured a rotating bezel capable of locking and became the standard for aviation professionals. A rotating bezel can be used to measure speed, distance, meeting times, a pulse rate and meter times.