<P> The term chronograph is often confused with the term chronometer . Where "Chronograph" refers to the function of a watch, chronometer is a measure of how well a given timepiece performs: in order to be labeled a chronometer the timepiece must be certified by the COSC, the official Swiss Chronometer testing institute, after undergoing a series of rigorous tests for robustness, accuracy and precision under adverse conditions . A simple watch, without the stopwatch functionality, can be certified a chronometer, as can a clock, for example a ship's clock be used for navigation . The terms are not mutually exclusive either, for instance the Omega Seamaster 300M Chronograph GMT Co-Axial is also a COSC certified chronometer </P> <P> Originally the term chronograph was mainly used in connection with artillery and the velocity of missiles . The Chronograph's main function is to allow a comparison of observation between a time base and, before the electronic stopwatch was invented, a permanent recording of the observer's findings . For example, one of the first applications of the chronograph was to record the time elapsed during horse races . </P> <P> Some more important uses of the chronograph include the Langley Chronograph, which is used by the US Navy to record, calculate, and analyse data given off by aeroplane launching catapults . Another famous usage of the chronograph was during all of NASA's Apollo missions to the moon, each astronaut was equipped with a fully functioning chronograph, the Omega Speedmaster . You can now find chronographs that are used to record heart beats within hospitals, calculate speed and / or distance on an athletic field, or even as simple as a cooking tool for the kitchen . </P> <P> Chronographs can be extremely complicated devices, but they all have the basic function of telling time, as they are watches, and of displaying elapsed time . Rieussec's chronograph was fairly simple . It was composed of two faces, a top and bottom face . The bottom face held a pool of ink, while the upper had a pen - like needle attached to it . When activated, the upper face pushed down on the lower face, while revolving around a central axis, which pulled the needle . This dragged the ink, in a circular fashion, recording the time elapsed by the line of ink that the motion created . There was room left for improvement, because Rieussec's chronograph was not easily ready for multiple uses . </P>

What do the three clocks on a watch mean