Seamaster Diver 300M 41.5 mm, steel on steel

The chronograph function is a mechanism for measuring time intervals. A chronograph watch can therefore be used to time events while displaying the time like any traditional watch.

Label given to a watch which has undergone precision tests and received a certificate from an official body (COSC).

The day of the month, displayed in a window on a watch dial at the 3 or 6 o’clock position, or within a subdial at 9 o'clock.

Decompression system which allows helium to escape from inside the watch when the watch is worn for professional use in pressure chambers. (Long-term underwater work, crude oil exploration, etc.)

Self-locking crown, screwed into the tube of the case, used for highly water resistant divers' watches.

A hand on a sub-dial which tracks seconds typically it completes a full rotation in one minute.

A bezel which turns in only one direction. Particularly useful for divers who cannot accidentally rotate it in the wrong direction, which could cause them to miscalculate their dive times. A rotating bezel makes it easy to measure elapsed time.