Swiss silver military deck watch Royal Navy H.S.↑2 Circa 1942

Silver chronometer for the British Hydrographic Service
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A Swiss silver deck chronometer for the British Hydrographic Service made by Vacheron Constantin SA in Geneva, circa 1942. The numbered case was crafted from silver, features the British military marking H.S.↑2 on the back lid, and an engine turned cuvette. The silver dial, marked Swiss, has Arabic hour numerals, an outer minute track, a subsidiary seconds dial at 6 o’clock and blued steel spade hands. Movement with a lever escapement, cut bimetallic compensated balance with gold poising screws, an index regulator with swan neck spring and micrometric screw. The case and movement share matching numbers, and the dial, case and movement are signed.
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Diameter: 60 mm
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Signed: Vacheron & Constantin Geneva
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Deck Watch
A deck watch is a precision watch used on the deck of boats for navigational purposes and point reading, to avoid disturbing the proper functioning of the marine chronometer, which remains in a specific area of the ship, chronometer room or captain’s cabin. 
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Guillaume Balance
The Guillaume balance is a compensated bimetallic balance, made of anibal (an alloy of steel and nickel) and brass, after Dr Charles-Edouard Guillaume (1861-1938), with which the middle temperature error is practically eliminated. The middle temperature error (or Dent’s anomaly) is the difference between the rate of a chronometer at the mean temperature and the average of the rates at extreme temperatures. Watchmakers have used this balance since 1904.