English chronometer with spring detent escapement Circa 1822

Heavy silver pocket watch by Parkinson & Frodsham
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A heavy English pocket chronometer with spring detent escapement and resilient stud, circa 1822. This device was probably intended to let the hairspring breathe more evenly in the style of the Breguet overcoil.
The case is silver, tiered, and polished with the case maker’s punch mark CL (Charles Lupton, 6 St. James’s Place, Clerkenwell). The signed enamel dial has Roman radial hours, auxiliary seconds, and gold spade hands. And the frosted, gilt, signed and keywind full plate movement has chain/fusee, bimetallic chronometer balance with four screws and two movable trapezoid weights, free-sprung blued balance spring with resilient stud, and chatoned diamond endstone on balance.
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Diameter: 59 mm
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Weight: 190 g
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Signed: Parkinson & Frodsham, Change Alley, London
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Parkinson & Frodsham,
In 1801 William James Frodsham, son of William Frodsham the Younger and William Parkinson founded the company that was to become famous as Parkinson & Frodsham at 4 Change Alley, Cornhill, in London. The two partners decided to specialize in pocket and marine chronometers; their business location was perfect for that because the coffee houses in the vicinity, such as Garroway’s, were frequented by captains, merchants and sales representatives of foreign trading houses who came to make their transactions. Very soon, the company did not only supply the British Admiralty with their goods but exported them to the whole of Northern Europe.