Swiss silver deck watch made for the German market Circa 1905

Silver deck chronometer with power reserve
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A very fine Swiss, early, silver, deck and pocket lever chronometer destined for observatory trial, with a 36 hour power reserve indicator and Guillaume balance, circa 1905. Accompanied by the extract from the archives. Made in 1905 for the German market, sold on September 15th, 1911. A polished case, hinged silver cuvette. Heavy, solid silver dial, bold champlevé radial Roman numerals, outer champlevé minute track, champlevé power reserve sector below 12 o’clock, champlevé subsidiary seconds. Blued steel spade hands.
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The movement numbered twice, 18 jewels, counterpoised straight line lever escapement, Anibal brass Guillaume balance with winged arms, gold and platinum temperature adjustment screws, blued steel Breguet balance spring with inner and outer terminal curves, diamond endstone, swan neck micrometric regulator, Patek, Philippe 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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The dial is slightly oxidized.
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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 bi metallic 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. Thus, it equals zero at only two temperatures, causing the secondary error. Countless attempts were made to eliminate Middle Temperature Error, usually by means of auxiliary compensation devices.
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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 bi metallic lamina, makes its expansion close to quadratic. Balances with bi metallic 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. A very fine example of a Patek Philippe deck watch from a small series, all destined for Observatory trials. Almost all were cased in silver; one example is known in gold. This watch is also interesting as an example of the early use of the Guillaume balance, it also has the early form of mechanism for the power reserve indication using a rack and sprung pivoted pinion mounted on the backplate of the movement.