Heavy English silver pair cased pocket chronometer Circa 1813

Chronometer in silver pair cases by John Brockbank 
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A heavy English silver pair cased pocket chronometer, circa 1813. Chronometer movement with spring detent escapement in manner of Earnshaw, very rare special balance, cylindrical platinum weights and trapezoidal bimetallic weights, helical hairspring, screwed gold chatons, diamond endstone, splendidly decorated cock. White enamel dial with Roman numerals and gold hands.  Plain cases. Comes with original signed watchpaper, matching London hallmarks from 1813, maker’s mark TH for Thomas Hardy, matching case, dial and movement number, dial and movement signed.
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Diameter: 60 mm
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Weight: 176 g
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Signed: Brockbanks London 770
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John Brockbank was apprenticed as a watchmaker by Joseph Harding in London from 1761. Together with his brother Myles, he belonged to the Clockmakers Company and made the finest chronometers.