Swiss gold chronograph with 30-minute register Circa 1910

Gold open faced lever chronograph by Vacheron & Constantin
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A fine and very rare Swiss 18 carat gold open faced chronograph keyless lever pocket watch with 30-minute register, circa 1910. Frosted gilt movement, 23 jewels, straight-line lever escapement, cut bimetallic compensation balance, blued steel Breguet balance spring, swan-neck micro-regulation, visible chronograph work. Gold hinged cuvette. White enamel dial with Breguet numerals, outer minute track with Arabic five-minute numerals, fifths of a second divisions, outermost blue red and blacked base 1000 meters tachometer scale, subsidiary seconds, 30-minute register at 12, original gold spade hands. Polished case. Dial, case, cuvette and movement signed, case and movement numbered.
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Diameter: 52 mm
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Signed: Vacheron & Constantin Genève