Swiss gold watch set in US 20 Dollar gold coin dated 1904 Circa 1980

Gold lever coin watch by Vacheron & Constantin
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A fine Swiss 18K extra thin keyless coin watch set into a 20 Dollar U.S. coin of 1904, circa 1980. The hinged watch within the coin opened by a push-piece concealed in the band. Champagne dial with black indexes. Blued steel bâton hands. A rhodium-plated movement, 17 jewels, straight-line lever escapement, monometallic balance, self-compensated balance spring. Signed on dial, case and movement.
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Diameter: 34 mm
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Signed: Vacheron & Constantin  Genève
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The case is oxidized.