From Wikipsedia Exeter Cathedral article:
The clock is one of the group of famous 14th- to 16th-century astronomical clocks to be found in the West of England. Others are at Wells, Ottery St Mary, and Wimborne Minster.
The main, lower, dial is the oldest part of the clock, dating from 1484. The fleur-de-lys 'hand' indicates the time (and the position of the sun in the sky) on a 24-hour analogue dial. The numbering consists of two sets of I-XII Roman numerals. The silver ball and inner dial shows both the age of the moon and its phase (using a rotating black shield to indicate the moon's phase). The upper dial, added in 1760, shows the minutes.
The Latin phrase Pereunt et Imputantur, a favourite motto for clocks and sundials, was written by the Latin poet Martial. It is usually translated as "they perish and are reckoned to our account", referring to the hours that we spend, wisely or not. The original clockwork mechanism, much modified, repaired, and neglected until it was replaced in the early 20th century, can be seen on the floor below. The door below the clock has a round hole near its base. This was cut in the early 17th century to allow entry for the Bishop's cat to deter vermin that were attracted to the animal fat used to lubricate the clock mechanism.
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