Speedmaster 42 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.

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

A tachymeter watch has a function for measuring speed. It is a chronograph with a graduated dial on which speed can be read in kilometres per hour based on a 1000 metre distance.