built around 1330, was one of the earliest recorded that struck the hours. In 1335, Galvano Fiamma wrote: The astronomical clock designed by Richard of Wallingford in 1327 and built around 1354, also struck 24 hours. Some rare clocks use a form of striking known as "Roman Striking" invented by Joseph Knibb, in which a large bell or lower tone is sounded to represent "five", and a small bell or high tone is sounded to represent "one". For example, four o'clock would be sounded as a high tone followed by a low tone, whereas the hour of eleven o'clock would be sounded by two low tones followed by a high tone. The purpose is to conserve the power of the striking train. For example, "VII" would be a total of three strikes instead of seven, and "XII" would be four strikes instead of twelve. Clocks using this type of striking usually represent four o'clock on the dial with an "IV" rather than the more common "IIII", so that the Roman numerals correspond with the sequence of strikes on the high and low bells. One small table clock of this type sold from the George Daniels collection at Sotheby's on 6 November 2012 for £1,273,250. Countwheel Two mechanisms have been devised by clockmakers to enable striking clocks to correctly count out the hours. The earlier, which appeared in the first striking clocks in the 14th century, is called "countwheel striking". This uses a wheel that contains notches on its side, spaced by unequal, increasing arc segments. This countwheel governs the rotation of the striking train. When the striking train is released by the timekeeping train, a lever is lifted from a notch on the countwheel; the uneven notches allow the striking train to move only far enough to sound the correct number of times, after which the lever falls back into the next notch and stops the striking train from turning further. The countwheel has the disadvantage of being entirely independent of the timekeeping train; if the striking train winds down, or for some other reason the clock fails to strike, the countwheel will become out of synch with the time shown by the hands, and must be resynchronized by manually releasing the striking train until it moves around to the correct position. Rack striking In the late seventeenth century, rack striking was invented. Rack striking is so called because it