Page 307 - A205-Flipbook

Navigation watch: Longines rarity, siderograph \u201EAero\u201C Marine Nationale Aeronotique Navale with double split-seconds,\u000ANr.6425246, Ref.6081, ca. 1939/40\u000ACa. \u00D894mm, ca. 545g, aluminium/steel case, screwed, back completely signed and numbered, high end precision calibre 21.29, signed silvered and numbered two-coloured dial, power reserve indicator, 3 central seconds hands, 2 of them with split-se- conds, in working order and in very good condition, absolute rarity. The sister watch 6425248 was auctioned in Geneva in 2004 and sold for 28,680 Swiss Francs (source: https://www.cortrie.de/go/Z8B). A siderograph is a combination of watch and navigation instrument and keeps a reference time corresponding to the time at 0\u00B0 Greenwich longitude. This precision instrument was stored in a wooden box, which centrally contained an aluminium plate with 5 springs that holds the measuring instrument in a suspended position. The holes for attaching the springs are located on the bottom of the case. The Longines siderograph was originally developed in 1938 to help with aircraft navigation. The instrument measures Greenwich sidereal and local time in hour angles, minutes and angular minutes. Its accuracy and precision made the siderograph the measure of all things in marine chronometry. It allowed the navigator to operate at night in the same way as during the day, far surpassing the systems of Weems and Lindbergh, as both depended on the time signals. The siderographs were equipped with the 2129 chronometer calibre, which was the most precise movement Longines possessed at the time. In addition, a split-seconds and an anti-magnetic beryllium lever were integrated and the movement was fitted into a hardened aluminium case. This material was perfectly suitable for aeronautical and maritime purposes due to its weight and non-iron character. Versions were available with one and (extremely rare) as here with two split-seconds!\u000ACortrie Uhren- und Schmuckauktionen 305\u000A