Silver watch with differential dial by John Bushman

Silver pair cased watch with differential dial by John Bushman, London, c.1700. The silver outer case is decorated with a simple repoussé pattern and engraved with the name 'James Bann', the inner case engraved with the initials JB. 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 'Bushman London'. Steel minute hand. Movement with verge escapement, tulip-shaped pillars, and backplate signed 'John Bushman 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. 120