Historically important split-seconds chronograph Circa 1950

Stainless steel chronometer with chronograph and recorder by Ulysse Nardin
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A fine and historically important, large Swiss stainless steel open-faced split-seconds chronograph keyless lever pocket chronometer with instantaneous 30-minute recorder, circa 1950. One from a series of 402. Rhodium-plated movement, Geneva striping, and oeil-de-perdrix decoration, 26 jewels, straight-line lever escapement, high-frequency Anibal-brass Guillaume balance, blued steel Breguet balance spring, micrometer index regulator. Detachable stainless steel cuvette. White enamel dial with painted Arabic numerals, outer minute track with Arabic five minute/second numerals, extreme outer chronograph ring divided into 1/5th and 1/10th of a second, subsidiary seconds, and 30-minute register, original black steel Breguet hands. Polished case with screwed-down case back engraved Arch. R. Sartorio, 1951, N. 127346, chronograph button on the winding crown and push-piece in the band for the split-seconds function. Dial, case, and movement signed, dial and case numbered. Accompanied by the original Bulletin de Marche of the Milan Observatory 1962 and the Genova Observatory 1967 and a letter of authenticity.
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Diameter: 65 mm
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Signed: Chronomètre Ulysse Nardin Locle Suisse Federazione Italiana Chronometristi Swiss
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This watch was tested by the Osservatorio Astronomico di Milano and the Federazione Italiana Cronometristi and was used as the manual second official timekeeper during the swimming events at the 1960 Rome Olympics as a backup for the automatic electronic timekeeper. The former owner of this watch was Arch. Renzo Sartorio who was the official timekeeper from the Federazione Italiana Cronometristi.