Swiss gold chronometer made for the English market Circa 1850

Gold chronometer with unusual banking for the detent
–
A fine and rare Swiss, 18K gold pocket chronometer with unusual banking for the detent, circa 1850. Made for the English market. An engine-turned and polished case, master mark PM. Hinged gold cuvette.
White enamel dial with radial Roman numerals, outer minute track, subsidiary seconds. Blued steel spade hands. A frosted gilt movement, half-plate, fusee and chain with Harrison’s maintaining power, Earnshaw type chronometer escapement with spring footed detent, spring footed banking arm parallel to the detent, free-sprung cut bimetallic compensation balance with gold temperature and meantime adjustment screws, blued steel helical balance spring, diamond endstone. Dial and movement signed.
–
Diameter: 48 mm
–
Signed: William Mottu  Genève
–
The case is slightly rusted
–
A well-known family of watchmakers working in Geneva in the second half of the nineteenth century, known, among other things, for supplying movements to E.J. Dent in London.
–
Ad. Mottu (1830 – 1831), was an eminent finisher and maker of balance- springs. At the Geneva Exposition in 1828, he presented a series of spherical balance-springs, and in 1829 he signed a petition for the construction of a new observatory.