English chronometer with spring detent escapement Circa 1856

Gold exquisite pocket watch by Charles Frodsham
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An exquisite English pocket chronometer with 24h power reserve indicator, spring detent escapement and duo-in-uno balance spring, circa 1856.
18 Carat gold, consular case, florally engraved, with case maker’s punch mark RO (Richard James Oliver, London). Signed enamel dial with radial Roman hours, auxiliary seconds, 24h power reserve indicator, and blued spade hands. Chatoned, signed, keywind, frosted gilt 2/3 plate movement, with chain/fusee, gold screw compensation balance, free-sprung, blued duo-in-uno balance spring, and chatoned diamond endstone on balance.
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Diameter: 49 mm
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Weight: 90 g
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Signed: Charles Frodsham, 84 Strand London
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Duo-in-uno hairspring
Duo-in-uno hairspring is a combination of Helical and spiral. It has an “up-down” indicator and sub-seconds. It also has a disconnect mechanism that disengages the winding when the bezel is closed.
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Charles Frodsham (1810-1871)
Frodsham was a maker of very fine watches, originally of the Strand, London, and then New Bond Street. His best quality watches bear the letters AD.Fmsz, which is interpreted as 1850, the year he bought J.R. Arnold’s estate after his death; the firm was known for a short period as Arnold and Frodsham. He conducted many experiments with compensated balances and the balance spring to discover their underlying principles; he also wrote several papers on technical subjects.