Chronograph

A watch indicating hours, minutes and seconds combined with a mechanism whose hand can be started, stopped and returned to zero on demand to measure a duration to one fifth, tenth or even hundredth of a second. Subcounters for the minutes and hours (usually 30 minutes and 12 hours) totalise the number of revolutions by the chronograph hand. The accuracy of these recorded times can only be guaranteed if the chronograph has satisfied the criteria of the "chronometer" label.
The first chronographs deposited drops of ink on their dial; this no longer being the case, strictly speaking a chronograph should be called a chronoscope.

See complication.