Historically important English gold chronometer Circa 1861

Miniature open faced pocket chronometer by John McLennan
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An extremely rare and historically important English 18 carat gold miniature open faced pocket chronometer with power reserve, circa 1861-1862. Gilt finished3/4 plate movement, spring detent escapement, bimetallic compensation balance, duo in uno helical hairspring. 18 Carat gold cuvette. White enamel dial with Roman numerals, blued steel hands, outer minute divisions, two subsidiary dials for 24 hours power reserve and constant seconds. Hinged engine turned case back, ribbed band. Case and cuvette stamped with casemaker’s mark ‘RR’ and London date letter for 1861/62, movement signed and numbered. International Exhibition 1862, Awarded Prize Medal Great Skills & General Excellence.
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Diameter: 26.4 mm
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Signed: John McLennan London