Probably the oldest working clock in the world is in Salisbury Cathedral, England. It is the oldest clock in England and is very likely the earliest mechanical clock in complete and working condition in the world.
It was made in or before 1386. Cathedral accounts for that year include a document concerning the provision of funds for maintaining a "clocke".
The clock was constructed entirely of hand-wrought iron. It was originally controlled by a verge escapement and foliot balance. But, to increase accuracy, this was altered at some later date by the provision of a pendulum escapement. There was no dial; there were no hands; the clock struck the hour on the hour. Another clock, presumably built by the same craftsmen as the one at Salisbury, struck the quarter hour as well.
The clock was rediscovered, after lying in obscurity, in 1929, after which it was established without a doubt as the earliest clock in England. In 1931, it was cleaned up and set up in the north transept of the cathedral, but was not in working condition. In 1956, it was finally repaired and restored to its original condition by the replacement of what was left of the pendulum by a verge and foliot balance such as it originally had.
The clock, made over 600 years ago, has been in the same location for longer than any other similar time piece.