English gold open faced pocket chronometer Circa 1825-1826

Gold chronometer with Peto cross detent escapement by Brockbanks
–
A very fine, extremely rare English 18 carat gold open faced pocket chronometer, Hallmarked London 1825-1826. Matte gilt 3/4 plate movement with detachable plate for the barrel, cylindrical pillars, third, fourth and escapement pivots with jewels in screwed gold chatons, fusee and chain, Harrison’s maintaining power, Peto cross detent escapement with brass escape wheel, adjustable steel passing spring, three armed bimetallic compensation balance with wedge shaped brass weights retained by steel plates and screws, free movement of the bimetallic sectors limited by small screws in the free ends, steel timing screws, blued steel flat balance spring, diamond endstone, empty fixing holes on the barrel bridge for the amplitude limiting device. Fixed gold cuvette engraved M.K. Hindmarsh. White enamel dial with Roman numerals, outer minute track, large subsidiary seconds and original gold Breguet hands. Engine turned case, mastermark WW, flat band, the back with small central engraved monogram. Movement signed.
–
Diameter: 51 mm
–
Signed: Brockbanks London
–
An amplitude limiting device consisting of a spring loaded pivoted lever, was once fitted to the barrel bridge of this watch, the fixing holes remain. Above a certain range of amplitudes, the expanding balance spring would push the lever sideways onto the path of a small steel piece carried on a balance crossing.
–
The Peto’s Cross Detent Escapement. Most surviving examples of the cross detent escapement are in chronometers signed Brockbanks. The escapement was invented by James Peto, who worked for the Brockbanks, around 1783-1784. 
–
John and Myles Brockbanks, pioneers of chronometry, were succeeded by their nephews, also named John and Myles.