chronoscope

from WordNet (r) 3.0 (2006)

chronoscope
    n 1: an instrument for accurate measurements of small intervals
         of time

from The Collaborative International Dictionary of English v.0.48

Chronoscope \Chron"o*scope\, n. [Gr. ? time + -scope.]
   An instrument for measuring minute intervals of time; used in
   determining the velocity of projectiles, the duration of
   short-lived luminous phenomena, etc.
   [1913 Webster]