Rare Swiss yellow gold chronomètre royal pocket watch Circa 1900

Gold open faced pocket watch
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A rare Swiss 18 carat yellow gold chronomètre royal keyless pocket watch, circa 1900.
A polished case, engine turned case back with a hinged gold cuvette. White enamel dial with bold radial Roman numerals, outer minute track, subsidiary seconds dial and yellow gold spade hands. Frosted gilt movement, 18 jewels, wolf’s tooth winding, straight line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, swanneck micrometer regulator. Dial, case, cuvette and movement signed.
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Diameter: 57 mm
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Thickness: 15 mm
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Signed: vacheron & Constantin  Genève