Lot 71

Longines Watch Co.

Siderograph

An extremely rare precision astronavigation chronometer with degree graduation, split seconds chronograph and 30h-power reserve display, so called "Siderograph" of the Service Hydrographique of the French Marine Nationale

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The Longines Siderograph was originally invented in 1938 to assist navigation in airplanes. The instrument measures Greenwich Sidereal or Mean Time in hour angles, minutes and minute arcs; its accuracy and precision make the Siderograph the ultimate in marine chronometry. It allows the navigator to operate at night as well as during the day and surpassed the Weems and Lindbergh systems for nocturnal navigation by far, because both systems relied heavily on radio time signals. The Siderographs were equipped with chronometer calibre 21.29, at the time the most accurate movement Longines possessed. A split seconds mechanism and an anti-magnetic beryllium pallet fork were added and the movement was fitted in heat-toughened aluminum case; this material was perfectly suited for aeronautic and maritime purposes because of its light, nonferrous nature.