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]WordNet (r) 3.0 (2006):
chronoscope n 1: an instrument for accurate measurements of small intervals of time