Fine Swiss yellow gold chronograph with register Circa 1900

Yellow gold chronograph with register
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A fine Swiss yellow gold chronograph with register and tachymeter open faced keyless chronometer watch, circa 1900, manual good quality mercury gilt lever movement, cut bimetallic balance with gold peripheral timing screws and blued Breguet balance spring with terminal curb, swan neck micrometric regulation system.
Whiteenamel dial, black Arabic numerals, two subsidiary dials for constant seconds and 30-minute register, inner minute and 1/5 seconds divisions, outer tachymeter scale in blue, red and black, 18k polished yellow gold case, case, dial and movement signed.
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Diameter: 51 mm
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Signed: Vacheron Constantin Genève Suisse