The term chronometer was coined from the Greek words chronos (meaning time) and meter (meaning counter) in 1714 by Jeremy Thacker.
A marine chronometer is a timepiece that is precise and accurate enough to be used as a portable time standard.
When first developed in the 18th century, it was a major technical achievement, as accurate knowledge of the time over a long sea voyage is necessary for navigation, lacking electronic or communications aids.
Modern marine chronometers can be based on quartz clocks that are corrected periodically by GPS signals or radio time signals (see radio clock). These quartz chronometers are not always the most accurate quartz clocks when no signal is received, and their signals can be lost or blocked. However, there are quartz movements, even in wristwatches such as the Omega Marine Chronometer, that are accurate to within 5 or 20 seconds per year.At least one quartz chronometer made for advanced navigation utilizes multiple quartz crystals which are corrected by a computer using an average value, in addition to GPS time signal corrections .