Swiss gold chronograph watch with tachy scale Circa 1916-1920

Gold pocket watch with chronograph by Vacheron & Constantin
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Very fine and rare hunting cased, keyless-winding Swiss pocket watch with a single push-piece for the chronograph, 30-minute counter and tachy scale, circa 1916-1920.
Polished 18K gold case. Outstanding, multi-coloured enamel dial for the chronograph with Breguet radial hours, outer minutes/seconds track with black Arabic five minutes/seconds numerals, subsidiary dial for the seconds, 30 minutes recorder, tachy scale, and spade hands. Gilded brass 2/3 movement with gold screw compensation balance, going barrel, straight-line lever escapement, cut bimetallic balance, blued steel hairspring with a terminal curve, and an index regulator with a swan neck spring and a micrometric screw. Case, dial and movement signed.
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Diameter: 53 mm
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Weight: 110 g
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Signed: Vacheron & Constantin, Genève