French 18 carat open faced cylinder pocket watch Circa 1820

Gold watch with short chain and key
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A thin French 18K gold pocket watch with short gold chain and ratchet key, circa 1820. An engine-turned case with a hinged gold cuvette. Silver, engine-turned dial, eccentric chapter ring with radial Roman numerals, outer minute track and gold Breguet hands.
A matte gilt, Lepine calibre movement, four jewels, cylinder escapement, three-arm balance, blued steel flat balance spring, and an index regulator.
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Diameter: 51 mm
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Signed: Sergent  Paris