Prest. A highly rare and unusual 18K gold openface splittable seconds watch with sector time indication

Prest. A highly rare and unusual 18K gold openface splittable seconds watch with sector time indication
Signed Thomas Prest, Chigwell, No. 527, stamped with London date letter for 1840
With full plate gilt-finished keywound movement, bimetallic compensation balance, diamond endstone, the engine-turned gilt dial with engraved scroll and foliage decoration, two fan-shaped apertures for the wandering Arabic minutes and Roman hours, enlarged subsidiary seconds dial with two splittable hands, the hands split/one hand stopped by depressing a button in the pendant, balance locking lever underneath the dial, in engine-turned circular case, case stamped with casemaker's initials HH and London date letter for 1840, movement signed and numbered
52 mm. diam.