Chronometer

n.
  1. An instrument for measuring time; a timekeeper.
  2. A portable timekeeper, with a heavy compensation balance, and usually beating half seconds; -- intended to keep time with great accuracy for use an astronomical observations, in determining longitude, etc.
  3. (Mus.) A metronome.
    4. Box chronometer .
    See under Box.
    Pocket chronometer ,
    a chronometer in the form of a large watch.
    To rate a chronometer .
    See Rate, v. t.