The Congreve Rolling Ball Clock was originally invented by an English scientist Sir William Congreve and patented in 1808. This method of operation of the clock is an alternative to the pendulum. Regulation is achieved by the traverse of a ball along the zig zag grooves on an inclined plane. The ball trips the escapement at the end of each traverse reversing the slope of the platform. The principle of the clock is such that the accuracy of the timekeeping is limited to =?- 3 minutes per day. This is not a reflection of the quality of the manufacture but the fact that the temperature changes, dust on the track and even staic electricity give rise to variations. The 8 day movement is fusee-driven, gold-plated and is protected by a rectangular glass cover edged in wood matching the base. The dials are silver plated and the clocks is available in two configurations; the original three dial version showing the hours minutes and seconds seperately as shown and a single dial version(see stock code S202G). This model is a limited edition and only 25 are made each year for worldwide distribution. Dimensions are H 360mm (14 inches); W290mm (11.5 inches); D 275mm (10.75 inches). Stock code S203G ?4700.00.