The internal chronometer was a part of a Soong-type android's construction. It functioned as a timekeeping device and could be switched off. (TNG: "Timescape") The Intrepid-class starship USS Voyager also had internal chronometers. (VOY: "Relativity")
In 2369, Data's internal chronometer was stopped by the solanogen-based lifeforms when they abducted the android. When comparing his internal chronometer to the USS Enterprise-D's chronometer, Data realized that he had been off the ship for more than ninety minutes. (TNG: "Schisms")
Later that year, after Counselor Deanna Troi saw Captain Picard, Data, and Geordi La Forge "frozen in time", Data checked his internal chronometer but couldn't find any discrepancy between his chronometer and the ship's computer. This experience and the crew's rescue of the Enterprise-D from a situation in which it, too, was "frozen in time" led Data to conduct experiments regarding his perception of time, based on the aphorism "a watched pot never boils." His experiments led him to believe that he was not capable of perceiving time any differently than his internal chronometer, but Commander William T. Riker noted that Humans did not have internal chronometers and suggested that he shut it off. (TNG: "Timescape")
In 2370, Data's dream program caused him to oversleep, but it was not due to a problem with his internal chronometer. (TNG: "Phantasms")
In 2375, space-time fractures inside Voyager continually grew stronger causing temporal paradoxes throughout the ship. Internal chronometers showed that decks 9 and 13 had different times. Time passed more quickly in some parts of the ship and slowed down in others. This explained why food replicated in the mess hall less than an hour beforehand had already spoiled and Janeway's coffee tasted like it was three days old. (VOY: "Relativity")