From the standpoint of navigation, the chronometer was one of the most important inventions of the 18th century. While this instrument looks a little elaborate for rough fieldwork, it performed well as long as it was kept wound. Note that the dial is calibrated in 12-hour increments rather than the 24-hour Greenwich Mean Time system used today for locational calculations. Much of modern naval terminology stems from the earliest nautical uses of the chronometer. The ship's bell, by which time was noted, was struck at specific intervals ("eight bells" denoted the passage of four hours), a level of accuracy not possible prior to the chronometer. And "watches," or the positions of responsibility for maintaining the ship's course during four-hour intervals, were also regulated bv the new device.
--John Logan Allen