Swiss silver split seconds chronograph lever watch Circa 1930

Silver pocket watch by Vacheron & Constantin
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A very fine and extremely rare Swiss keyless silver pocket lever chronometer with split seconds chronograph, Bulletin de Première Classe instantaneous 30-minute register, circa 1930. Gilt movement, 28 jewels, straight line lever escapement, Guillaume balance with gold timing screws, blued steel Breguet balance spring with double overcoil, swan-neck micrometer regulator.
Solid case, polished, hinged silver cuvette, back engraved with a military inventory number.
White enamel dial with upright dauphine numerals, outer minute track with five-seconds/minute Arabic markers, outermost fifth second timing scale, sunk subsidiary seconds, 30-minute register at 12. Blued steel Breguet hands. Case and movement signed.
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Diameter: 51 mm
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Signed: Vacheron & Constantin, Genève Suisse