Swiss chronometer with unusual banking for detent Circa 1850

Gold pocket chronometer made for the English market by William Mottu
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A fine and rare Swiss 18 carat gold open faced pocket chronometer with unusual banking for the detent made for the English market, circa 1850. Frosted gilt, half plate movement, fusee and chain with Harrison’s maintaining power, Earnshaw type chronometer escapement with spring footed detent, spring footed banking arm parallel to the detent, freesprung cut bimetallic compensation balance with gold temperature and mean time adjustment screws, blued steel helical balance spring, diamond endstone. White enamel dial with Roman numerals, outer minute track, subsidiary seconds and original blued steel spade hands. Engine turned and polished case, mastermark PM. Gold hinged cuvette.  Dial and movement signed.
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Diameter: 48 mm
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Signed: William Mottu Geneve