A uni-directional rotating bezel is a type of watch bezel that can only be turned in one direction. It is typically used on dive watches as a safety feature, allowing the wearer to measure elapsed time underwater. The bezel is marked with a series of hash marks, usually in minute increments, so that when the bezel is turned, the wearer can easily tell how much time has elapsed. The bezel is designed to prevent accidental rotation in either direction, which could lead to inaccurate elapsed time measurements.
