Swiss gold perpetual calendar, moon phase watch Circa 1918

Gold open faced lever pocket watch
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A rare yellow gold open faced perpetual calendar lever watch with moon phases, circa 1918. Keyless lever movement, white enamel dial, Arabic numerals, outer minute track, subsidiary dials for date combined with constant seconds, month, day and ages and phases of the moon, blued steel spade hands, 18k yellow gold case and cuvette, dial and movement signed.
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Diameter: 54 mm
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Signed: Patek Philippe & Cie  Genève
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Accompanied by a Patek Philippe presentation case and an Extract from the Archives confirming date of manufacture in 1918 and date of sale on April 4th, 1945.