Swiss 18 carat yellow gold keyless jump-hour watch Circa 1928

Gold open faced lever dress watch
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A very fine and extremely rare Swiss, 18K yellow gold, keyless, jump-hour watch, circa 1928. Sold on August 6, 1947. Accompanied by the Extract from the Archives.
A polished case, hinged gold cuvette. Matte champagne dial, aperture for jump-hour with Arabic numerals on matte silver reserve, outer minute track with black five-minute Arabic numerals, subsidiary seconds. Blued steel Breguet hands. A rhodium-plated movement, 18 jewels, wolf’s tooth winding, stamped twice with the Seal of Geneva quality mark, cut bimetallic compensation balance adjusted to heat, cold, and isochronism and five positions, straight-line lever escapement à moustache, blued steel Breguet balance spring, spring-loaded micrometre regulator. Dial, case and movement signed.
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Diameter: 46 mm
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Signed: Patek, Philippe & Co.  Geneva
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Patek Philippe watches with jump hour mechanisms are very rare in any form. Although the company started experimenting with them as early as the 1880s, only a handful was made, usually on special order. For instance, the watch with the preceding number, 820812, also with a jump hour feature, was made on the express order of Cowell & Hubbard Co., in Cleveland, Ohio. It was not until 1989 that Patek Philippe put a watch with a jump-hour feature into full production when the Ref. 3969 wristwatch was made to celebrate the 150th anniversary.