Rare Swiss 18K gold watch with chronograph Circa 1916

Gold open faced watch in original box by Vacheron Constantin
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A very fine and rare, manual wind, 18K yellow gold, Swiss chronograph pocket watch with minute counter, circa 1916.
An 18K gold, special polished case with a beautifully integrated hinge. Enamel dial with Roman radial hours, outer minutes/seconds track, subsidiary dial for the seconds, 30-minute counter, and gold spade hands. Frosted gilt ankerchronometer movement with especially large chronometer balance, fine adjusting device, chronograph with register, straight-line lever escapement. Signature on dial, case and movement.
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Diameter: 51 mm
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Signed: Vacheron Constantin Genève Suisse