Unusual Swiss 18k gold open faced keyless lever Circa 1940

Gold keyless lever by Vacheron Constantin
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A fine and unusual Swiss 18 carat gold open faced keyless lever watch, circa 1940. Mechanical movement, 18 jewels, bimetallic compensation balance. Two-tone matte silvered dial with applied Breguet numerals, outer beady minute division and engine turned subsidiary dial for constant seconds. Case with snap on back, inside case back engraved 20 Nov. 1940, outside case back centered with monogram EG. Case, dial and movement signed, case and movement numbered.
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Diameter: 41 mm
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Signed: Vacheron & Constantin Genève Swiss