Swiss yellow gold keyless pocket watch chronometer Circa 1920

Yellow gold large keyless pocket watch
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A very fine and rare, large, 18 carat yellow gold keyless pocket watch chronometer. Made by  Vacheron & Constantin, Genève, Chronomètre Royal, Circa 1920.
Four-body, bassine and polished case with sunburst engraved case back with reserve clear for monogram and hinged gold cuvette signed. White enamel dial with bold radial Roman numerals, outer minutes track, large subsidiary seconds dial and yellow gold dagger hands.
Frosted gilt movement with wolf’s tooth winding, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring and swan neck micrometre regulator.
Dial, case, cuvette and movement signed.
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Diameter: 57 mm
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Signed: Chronometre Royal, Vacheron & Constantin, Genève