The clock runs on a turret clock electrical system. It was made by Billett and Johnston, still one of Britain's great turret clock manufacturers. The mechanism inside the tower is known as a turret clock. Peter Watkinson, turret clock maker and antique clock restorer, overhauled the clock. St. Olave's had a turret clock, parts of which still survive. Dent constructed a turret clock for the Great Exhibition of 1851. The turret clock, made by John Knibb, dates from 1690.. The turret clock is by Tucker of London, dated 1853. A clock tower is an architectural structure housing a turret clock. In 1792 Harrison installed the turret clock at University College, Oxford. The tower has also an historic turret clock that was installed in 1697. The church has a turret clock that John Briant of Hertford made in 1792. In 1867 the church received a new turret clock by Reuben Bosworth of Nottingham. Simmons of Warwick made the present turret clock in the west tower in 1865. Dover Castle Clock is a turret clock from the beginning of the 17th century.