Swiss chronometer with Guillaume-type balance Circa 1925

Gold precision lever with open face by Vacheron & Constantin
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A Swiss 18K yellow gold open faced keyless-winding lever pocket chronometer with Guillaume-type balance, circa 1925. Model, Chronomètre, with First Class Bulletin de Marche from the Astronomical Observatory of Geneva.
Gilded brass movement, going barrel, gold screwed-Chaton (setting) on the central wheel, straight-line lever escapement, compensated brass Invar Guillaume balance with gold and platinum poising screws, patented index regulator with a micrometric screw. Enamel dial with suspended Dauphine radial hours, outer minutes track, subsidiary dial for the seconds, and original pear hands. Round-shaped 18K yellow gold polished case.
Dial, case and movement signed. Accompanied by a copy of the invention patent.
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Diameter: 54 mm
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Signed: Vacheron & Constantin, Genève
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Movement-based on the Swiss invention patent No. 101 652, delivered on September 30, 1922, to Vacheron Constantin, Geneva, for a Raquette de montre.