A rare early 19th century gold and half-pearl watch ring

A rare early 19th century gold and half-pearl watch ring
The octagonal bezel with white enamel dial and black Arabic numerals and aperture revealing the rose-cut diamond balance wheel to the cylinder movement, within a half-pearl line and engine-turned border, the reverse with sliding plate revealing the key positions for the movement, hands and advance and retard, French or Swiss, circa 1810, finger size K