Swiss technically interesting large verge watch Circa 1770-1798

Open faced pocket watch by Jean Marc Allamand a Geneve
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A Swiss technically interesting, large verge watch with visible balance and a unique movement, circa 1770-1798.
Original silver case with punch mark and signed on the dome; very unusual and interesting gilt intact original movement with verge escapement; signed white enamel dial with Arabic numerals, keyhole and visible balance.
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Diameter: 57 mm
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Weight: 103 g
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Signed: Allamand