Swiss 18k gold lever with extra quality movement Circa 1911

Gold keyless watch with power reserve
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A very fine and rare 18K gold Swiss, keyless pocket lever chronometer with extra quality movement, power reserve and Guillaume balance, circa 1911. Made for an Observatory trial. Accompanied by an Extract from the Archives. Sold to Wright, Kay & Co., Detroit, on 30th September 1913. A polished, hinged back with engraved monogram. Hinged gold cuvette with engraved presentation inscription. White enamel dial, black Breguet numerals, outer minute track and red Arabic five minute numerals, subsidiary seconds, power reserve sector below 12. Gold Louis XV hands.

Movement with Geneva striping decoration, wolf’s tooth winding geared to an extra wheel operating the power reserve indicator, 21 jewels, counterpoised straight-line lever escapement, Guillaume balance with gold temperature screws and platinum mean time screws, eight adjustments, blued steel Breguet balance spring, swan-neck micrometre regulator, diamond endstone. Dial, case, cuvette, and movement signed, movement numbered twice.
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Diameter: 50 mm
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Signed: Patek Philippe & Cie  Genève
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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 a 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.