Swiss silver lever deck watch with indirect centre seconds Circa 1939

Silver lever deck chronometer by Ulysse Nardin
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A fine Swiss silver open faced lever deck chronometer with indirect centre seconds, circa 1939. Frosted gilt movement, 18 jewels, straight-line lever escapement, anibal-brass Guillaume balance, blued steel Breguet balance spring with terminal curve, micrometric regulator. White enamel dial with radial Roman numerals, outer Arabic minute and seconds ring with fifths of a second divisions and original blued steel spade hands. Solid case, polished, screw down back. Dial, case and movement signed, case and dial numbered.
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Diameter: 56 mm
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Signed: Ulysse Nardin Locle
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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.