Swiss silver deck watch made for the German market Circa 1906

Silver deck and pocket lever chronometer 
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A very fine Swiss, silver deck and pocket lever chronometer with 36-hour power reserve indicator and Guillaume balance, circa 1906. Made for the German market. Accompanied by the Extract from the Archives. A polished case, silver hinged cuvette. Heavy, solid silver dial, bold champlevé radial Roman numerals, outer champlevé minute track, champlevé up-and-down sector at 12, champlevé subsidiary seconds. Blued steel spade hands.
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Movement, 18 jewels, straight-line calibrated lever escapement, Anibal-brass Guillaume balance with winged arms, gold temperature adjustment screws and platinum mean time ones, special alloy Breguet balance spring inner and outer terminal curves, diamond endstone, swan-neck micrometric regulator, Patek, Philippe & Cie. keyless winding (Swiss patent 2680, 27 September 1890.) Dial, case and movement signed.
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Diameter: 60 mm
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Signed: Patek, Philippe & Cie  Genève
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Anibal (Acier au nickel pour balanciers): an alloy invented by Dr Charles Edouard Guillaume, exhibits unusual properties, both in terms of thermal expansion and in changes in elasticity. These properties are very different from those of two other famous alloys invented by Guillaume, Invar and Elinvar. Around 1900 Guillaume attempted to eliminate the so-called Middle-Temperature Error caused by the fact that the change of rate in a timekeeper with a steel-brass bimetallic balance is approximately a linear function of temperature, while the change of rate is caused by a change in the elasticity of a balance spring is approximately a quadratic function.
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So it equals zero at only two temperatures, causing a secondary error. Countless attempts were made to eliminate Middle-Temperature Error, usually by means of auxiliary compensation devices. In 1899, 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 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.