Chronometer

A chronometer is a devise used to track the passage of time.

Starships use chronometers to keep records of time passing, this can often be useful when something happens to the crew of a ship that causes them to loose track of time. When the USS Enterprise was attacked by the Ngultor consulting the chronometer informed the crew they had been incapacitated for forty-nine minutes. (EV comic: Flesh of My Flesh)

Chronometers of Constitution class starships in the 23rd century featured a bridge readout which displayed the time as a stardate and on a shipboard twenty-four hour clock. (TOS episode: The Naked Time)