English gold watch with Arnold-type spring detent escapement Circa 1798

Gold open faced chronometer watch
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A fine and rare English 18K gold open faced pocket chronometer with Arnold-type spring detent escapement, circa 1798. A polished case with London hallmarks for 1818-1819, fixed cuvette. White enamel dial, radial Roman hours, outer minute divisions, subsidiary dead-seconds and yellow gold pear hands.
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A hinged gilt-brass full plate movement, ringed cylindrical pillars, eight jewels of which three in screwed chatons, fusee with chain, Harrison‘s maintaining power, Arnold‘s spring detent escapement beating 18,000 beats per hour, the detent set in a slot cut in the backplate, a cut bimetallic compensation balance with internal and external temperature and meantime adjustment screws, free-sprung blued steel helical balance spring with terminal curves, diamond endstone, foliate engraved cock. Dial and movement signed.
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Diameter: 53 mm
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Signed: Paul Philip Barraud London
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The case and dial are custom-made and the movement has some replacements.
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The present watch was supplied by George Jamison, who was active from 1786 to 1810. He was one of the makers engaged to supply Barraud with chronometers. Jamison’s association with Barraud ended around 1798 or 1799. This watch was apparently fitted with an upgraded balance in 1818, at which time a new case was also made and a new dial fitted, probably because the original was signed by Jamison. 
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Paul Philip Barraud (1753-1820) was an eminent British watchmaker. In 1796 he entered into a partnership with William Howells and George Jamison to make chronometers based on Mudge’s original design. Howells, who had been Mudge’s junior worker and had been dismissed, brought with him important technical knowledge. To reduce production costs, they decided to use a single balance spring and Arnold’s ‘Z’ balance with a helical balance spring.