Swiss gold astronomic open faced lever watch Circa 1920

Gold watch with moon phases perpetual and lunar calendar
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A very fine and rare, Swiss astronomic, 18 Carat yellow gold keyless pocket lever chronometer, circa 1920. With a perpetual calendar, moon phases and lunar calendar. Hinged gold cuvette engraved with the technical details. White enamel dial with black Breguet numerals, outer minute track, subsidiary dials for the months and four year cycle, the date, day of the week, seconds combined with lunar calendar (in red), aperture for the phases of the moon. Black Breguet hands.

A rhodium plated movement, 21 jewels, wolf’s tooth winding, straight line moustache lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring with double overcoil, micrometer regulator.
Cuvette signed.
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Diameter: 52 mm
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Signed: Ed. Koehn Genève
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Edward Koehn (1839-1908) was the son of Karl Koehn, a watchmaker to the court of the Grand Duchy of Saxe-Weimar-Eisenach. He came to Geneva in 1859 and studied at the Ecole d’Horlogerie. In 1861, he began working at Patek Philippe, as a simple employee. After 15 years of loyal services, he became Director. In 1891, Edward Koehn left Patek and bought the Robert Ekegren firm. Koehn constructed very high quality flat and extra flat watches, repeating watches, chronographs, and flyback chronographs. The firm, at the Grand Quai, made watches for Tiffany, New York. On June 8, 1912, patented a watch with a hanging barrel and pendant winding, the Roseau. The Thermindex on the 13 February 1922.