English chronometer with spring detent escapement Circa 1850

Open faced pocket watch by William Gravell
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A heavy English pocket chronometer with spring detent escapement according to Thomas Earnshaw, circa 1850.
The case is 18 carat gold with case maker’s punch mark “JR”; the dial is off white enamel with Roman hours, a sunk subsidiary dial for the Arabic seconds and gold spade hands; the movement is a full plate movement with a chain/fusee and a bimetallic chronometer balance with 2 screws and 2 movable trapezoid weights. Dial and movement are both signed.
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Diameter: 54 mm
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Weight: 158 g
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Signed: William Gravell, London,