English: Omega Constellation Megaquartz F4.19 MHz chronometer, French Navy issue. The calibre 1525 movement uses an advanced 4.19 MHz quartz resonator (precisely 2²², or 4,194,304, hertz), giving an accuracy better than ± 5 seconds per year. The chronometer was designed at the request of the French Navy. It was available commercially at great expense but was predominantly used for military applications with the French Navy, who used the Marine Chronometer in the majority of their fleet. It was supplied in a mahogany box with brass fitting and was very much a case of function over form and built to the highest of military specifications including magnetic shielding. Each was numbered on a brass plaque and ran on two standard AA type batteries. The battery condition can be checked, and they can be exchanged one by one to keep the clock running. A set of batteries provided power for circa 2 to 3 years. The second hand advances in ½-second increments for optimal timing of angle measurements of celestial objects used in navigation.