Swiss indirect centre seconds deck chronometer Circa 1939

Deck watch with indirect centre seconds and Guillaume balance
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A fine Swiss staybrite brass keyless lever deck watch chronometer with indirect centre seconds and Guillaume balance, circa 1939. Frosted gilt movement, 23 jewels, straight-line lever escapement, the upper pivots of the escape wheel and the lever with gold endplates, anibal brass Guillaume balance, blued steel Breguet balance spring with terminal curve, micrometric regulator. Hinged staybrite cuvette. White enamel dial with Roman numerals, outer Arabic minute, seconds ring with fifths of a second divisions and original blued steel spade hands. Double body mahogany and brass deck box, the brass bowl with screwed bezel. Dial, case and movement signed.
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Diameter: 64 mm
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Signed: Chronomètre Ulysse Nardin Locle Suisse
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The Guillaume Balance. In 1899, Dr. Charles Edouard Guillaume noted that steel with an addition of 44.4% nickel had a negative square coefficient of thermal expansion. This alloy, combined with brass in bimetallic lamina, makes its expansion close to quadratic. Balances with bimetallic rims made of anibal (anibal, an alloy invented by Guillaume, stands for (Acier au Nickel pour BaLanciers) and brass are usually called Guillaume balances, or, as their inventor called them, integral balances. When combined with special balance springs, they exhibit remarkable temperature stability.