Swiss silver lever deck watch with power reserve Circa 1939

Silver open faced keyless watch
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A fine Swiss silver, keyless, circuit-break lever chronometer deck watch by Ulysse Nardin, Locle & Geneve, circa 1939. With power reserve indication and Guillaume balance. A silver bolt at 6 to activate the circuit breaking, insulated and non-insulated silver pins for transmitting the signal. Silver hinged cuvette. Matte silvered dial with radial Roman numerals, outer minute track, subsidiary seconds and 36-hour up-and-down scale. Blued steel spade hands. Frosted and gilt, 17 jewels, straight-line lever escapement, Anibal-brass Guillaume balance, blued steel Breguet balance spring, swan-neck micrometric regulator, escape wheel pinion fitted with a cam for contact- breaking each second. Dial, case and movement signed.
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Diameter: 64 mm
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Signed: Ulysse Nardin Locle & Geneve
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In a letter to the US Naval Observatory in 1910, Paul Nardin wrote that between 1883 and 1910 the company made only 50 circuit break survey chronometers for scientific institutions worldwide. The circuit-break (Survey) Chronometer was designed for surveying and mapping operations as well as solar observations and scientific experiments in remote areas, requiring accurate, audible time signals. The first circuit-break mechanism was installed in 1874 by the Negus brothers, chronometer makers from New York. Survey chronometers were superbly finished and adjusted, to meet the requirements of the surveying and scientific communities.