A chronograph is a timepiece capable of measuring discrete elapsed time units as well as telling time in a 12-hour format. In such a watch, each of these two separate time-keeping functions operates independently. This means that one typically contains a mechanism for regular time-keeping as well as a separate movement for the stopwatch, or elapsed time, function. A chronograph should be distinguished from a chronometer, which is a timepiece that is officially certified for its high degree of accuracy.
Pocket watch chronographs were produced as early as the 18th century but did not become popular until the 1820s. The term ‘Chronograph’ is often confused with the term ‘Chronometer’ which in some cases designates a watch that has received a precision certification. The Marine chronometer was an accurate timepiece used to enable celestial navigation.