Swiss stainless steel deck watch with power reserve Circa 1943

Lever deck watch with power reserve indication and Guillaume balance 
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A very fine Swiss stainless steel keyless deck lever chronometer with power reserve indication and Guillaume balance in the original three tier wooden deck box, circa 1943. Sold on October 21, 1943. Frosted gilt movement, 18 jewels, straight-line lever escapement, anibal brass Guillaume balance with blued steel Breguet balance spring, patented cam type micrometer regulator. Stainless steel cuvette. White enamel dial with bold Roman numerals, outer minute track, power reserve indicator below 12 o’clock, subsidiary seconds and original blued steel spade hands. Polished case, screwed down back. Dial, case and movement signed, case and movement numbered. Accompanied by the Bulletin de Marche.
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Diameter: 65 mm
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Signed: Ulysse Nardin Locle Swiss
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Guillaume Balance 
In 1899 Dr. Charles Edouard Guillaume noticed 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, on occasion not exceeding 1/50 second per day at 1oC.