Unusual French 18 carat gold pocket chronometer Circa 1867

Chronometer with Fahrenheit and Centigrade thermometer by Boitel
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A fine, rare and unusual French 18 carat gold open faced keywound pocket chronometer with Fahrenheit and Centigrade thermometer, circa 1867. Nickel finished movement, chain fusée, Earnshaw type detent escapement, bimetallic compensation balance, gold wedge shaped weights, helical hairspring, diamond endstone, freesprung regulator. Gold cuvette. White enamel dial with Roman numerals, aperture at 12 o’clock revealing the thermometer mechanism, calibrated for 0 to 100 Fahrenheit and -20 to +40 Centigrade, subsidiary seconds. Plain case. Movement signed.
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Diameter: 50 mm
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Signed: Hri Boitel Paris Exp.tion Universelle de 1867 Chronomètre