Swiss yellow gold keyless watch with tachometer Circa 1918

Gold open faced lever with chronograph
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A fine and rare Swiss 18K yellow gold keyless dress watch with chronograph, instantaneous 30-minute register and outer tachometer scale, circa 1918. The case with London import marks for 1939. Solid, polished bassine, concealed hinge. Hinged gold cuvette.

White enamel dial with black Breguet numerals, outer tachometer scale calibrated for 1000 meters, 30-minute register at 12, subsidiary seconds at 6. Gold spade hands. Frosted gilt movement, 21 jewels, straight line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, swan-neck micrometer regulator. Dial, case and movement signed.
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Diameter: 53 mm
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Signed: Vacheron & Constantin Genève