Swiss lever for the U.S. Army Corps of Engineers Circa 1918

Silver open faced lever chronograph by Vacheron & Constantin
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A fine and interesting Swiss silver open faced keyless lever chronograph pocket watch, circa 1918. Made for the U.S. Army Corps of Engineers. Frosted gilt brass movement, 20 jewels, straight-line lever escapement, cut bimetallic balance, blued steel Breguet balance spring, swan neck micrometrer regulator, chronograph with visible work, the button on the winding crown. Hinged silver cuvette. White enamel dial with bold upright luminescent Arabic numerals, outer Arabic minute and chronograph ring, subsidiary seconds, blued steel luminescent skeleton hands. Polished case. Dial, case and movement signed, case numbered.
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Diameter: 52 mm
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Signed: Corps of Engineers U.S.A. Vacheron & Constantin Genève