You searched for: “chronography
1. An instrument for graphic measurement and recording brief periods of time.
2. An instrument for recording time with extreme exactness; also, a watch or clock to which various mechanical devices are attached for the same purpose.

It is used in astronomical and other observations, in the timing of races, etc.

This entry is located in the following units: chrono-, chron- (page 3) grapho-, graph-, -graph, -graphy, -grapher, -graphia (page 18)