English silver watch with retrograde power reserve Circa 1855

Rare silver open faced watch with a retrograde power reserve
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An English rare silver open faced watch with retrograde power reserve, circa 1855, gilt plate, detent escapement, helical balance spring, Guillaume balance, silver cuvette.
White enamel dial, Roman numerals, subsidiary seconds, retrograde power reserve.
Silver engine-turned case with centered cartouche, cuvette signed and numbered.
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Diameter: 60 mm
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Signed: Laumain