Swiss silver chronometer for the Chinese market Circa 1840

Silver open faced pocket watch
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An unique pocket watch with spring detent escapement and centre seconds with half seconds jump made for the Chinese market, circa 1840.
A silver case, glazed movement, case maker’s punch mark FDB. Enamel dial, bridge movement, keywind, going barrel, bimetallic chronometer screw balance.
As far as we know this is the only known pocket watch with a precision movement with spring detent escapement that was ever produced for the Chinese market.
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Diameter: 55 mm