Precision watch with Guillaume type balance Circa 1917

Gold open faced precision lever by Vacheron Constantin
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A very fine and rare Swiss 18-carat gold open faced keyless lever precision watch with Guillaume-type balance, circa 1917. Gilt brass keyless lever movement, 21 jewels, wolf’s tooth winding, Anibal brass Guillaume type Integral Balance with gold and platinum poising screws, blued steel Breguet balance spring with double overcoil, swan neck micrometre regulator. Gold cuvette. White enamel dial with Arabic numerals, gold pear hands and subsidiary seconds Plain case. Case, cuvette, dial and movement signed. Accompanied by Geneva Observatory First Class Bulletin and Key Observatory Class A Chronometer certificate.
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Diameter: 55 mm
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Signed: Vacheron & Constantin Genève