Watch with differential dial by John Ferrers

Pair cased watch by John Ferrers c.1695. The outer case is covered in tortoiseshell and decorared with silver pins and disks. The inner case is of plain silver. The silver champlevé dial has a minute band around the outer edge, and a central rotating disc displaying the hours, marked I-XII. Between the minutes and the hour disc is a band with a repoussé trophy of arms and name plaque below, signed 'Ferrers, London'. Single steel hand. Movement with verge escapement, and signed on the backplate ‘Jno. Ferrers London’.

Although this watch has only a single hand which points to the minute markers, it is able to also read the hours thanks to the clever system it employs. The minute hand rotates clockwise once per hour, as standard. The central hour disc also rotates in the same direction, but at 11/12 the speed of the minute hand. This enables the correct portion of the hour to be read as it 'keeps up' with the rotating hand.

Clockmakers' Museum No. 1195