Very rare Swiss rose gold open faced chronograph Circa 1940

Rose gold chronograph keyless lever watch by Patek Philippe
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A very rare and attractive Swiss 18 carat rose gold open faced chronograph keyless lever watch, circa 1940. Retailed by Hausmann & Cie. Nickel finished lever movement, 23 jewels, bimetallic compensation balance, micrometer regulator. Rose gold dial, applied gold dot and Arabic numerals, outer Arabic five minute divisions and tachymetre scale, two subsidiary dials for 30 minutes register and constant seconds. Plain case, stepped bezel, snap on back, two rectangular chronograph buttons in the band. Case and movement signed by maker, dial signed by maker and retailer.
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Diameter: 46.5 mm
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Signed: Patek Philippe & Co Genève – Hausmann & Cie