Swiss 18 carat gold keyless pocket watch Circa 1925

Gold open faced pocket watch
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A Swiss 18 carat yellow gold open faced keyless pocket chronometer, made by Vacheron & Constantin in Geneva, circa 1925. A polished, plain case back with a white enamel dial with suspended Dauphine numerals, outer minute track, subsidiary seconds at 6 and blued steel Spade hands. A gilded brass movement, going barrel, gold screwed chaton on the central wheel, straight line lever escapement, cut bimetallic brass Invar compensated Guillaume balance with gold and platinum poising screws, blued steel hairspring with terminal curve, patented index regulator with micrometric screw. Signature on the dial, case and movement.
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Diameter: 54 mm
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Weight: 116 g
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Signed: Vacheron & Constantin, Geneva
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Accompanied by a copy of the invention patent.
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Movement based on the Swiss invention patent No. 101 652, delivered on September 30, 1922, to Vacheron Constantin, Geneva, for a Raquette de montre (Index regulator).