Exceptionally rare Swiss gold pocket chronometer Circa 1916

Gold full hunter made for the Russian market
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An exceptionally rare Swiss 18 carat yellow gold hunting cased keyless pocket chronometer made for the Russian market by Omega in Biel/Bienne, circa 1916. One of a series of only 60 examples of 20, grade DDR, full hunter movements produced. A solid, polished case with hinged gold cuvette. White enamel dial with bold Arabic hour numerals, an outer minute track, sunk subsidiary seconds at 6 o’clock and blued steel Breguet hands. A decorated nickel silver movement with 23 jewels, of which 18 in gold chatons, a Guillaume balance with gold and platinum timing screws, two diamond endstones, blued steel Breguet balance spring, an eccentric cam regulator and a gold wheel train. This watch was sold with a presentation box and certificate of authenticity.
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Diameter: 54.5 mm
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Signed: Ω Omega  Swiss
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The present watch is equipped with the famous DDR caliber and received a Bulletin de Première Classe from the Observatoire de Neuchâtel on December 20th, 1915. The DDR caliber is, without a doubt, one of the finest calibers produced during the 20th century and was largely responsible for Omega’s reputation as makers of the finest precision watches at the beginning of that century.
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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 the bimetallic lamina, makes its expansion close to quadratic. Balances with bimetallic rims made of Anibal (an alloy invented by Guillaume, which is short 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.