Swiss gold chronograph watch with pulsometer scale Circa 1915

Gold open faced keyless lever
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A rare Swiss 18 carat yellow gold open faced keyless chronograph pocket watch with register and pulsometer made by Vacheron & Constantin in Geneva, circa 1915. The polished case with a button in the crown for the start/stop and return-to-zero functions of the chronograph and a hinged gold cuvette. White enamel dial with Breguet hours, an outer minute and fifth of a second track with five minute numerals, outermost red pulsometer scale, subsidiary seconds at 6 o’clock, a 30 minute register and blued steel sword hands. Movement with 23 jewels, a 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: 54 mm
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Thickness: 13 mm
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Signed: Vacheron & Constantin  Genève
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The hands are partially replaced.