English chronometer with OZ balance by John Arnold Circa 1782

Extremely rare silver open faced pocket watch
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An extremely rare, important English Arnold chronometer – one of the earliest existing of the second kind – with OZ balance by John Arnold, circa 1782. Silver case with case maker punch mark ITP (John Terril Pain) and large lateral hinge. Enamel dial with radial Roman numerals, auxiliary seconds and blued spade hands. Full plate fire gilt, signed and numbered movement with eight jewels, chain/fusee, rounded pillars, Arnold’s spring detent escapement, OZ balance, blued free-sprung helical balance spring with both sides passing, very finely engraved pierced balance cock, and set diamond endstone on balance.
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Diameter: 53 mm
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Weight: 114 g
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Signed: John Arnold, London, Invt. et Fecit
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Provenance Gerd Ahrens Collection. Built-in 1782, this chronometer appears to be one of the first ever made with a spring detent escapement patented by John Arnold the same year as his famous OZ balance, with the first attempt of a helical spring with terminal curves. This must be considered a major testimony of early British chronometry.