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The Great Clock of Parliament (Big Ben) uses a pendulum to keep time. Fine adjustment of the pendulum is accomplished by adding old (pre-decimal) pennies to the pendulum. According to the website of Parliament, each 9.4 g penny is added to the pendulum in such a way that the clock mechanism speeds up enough to gain two fifths of one second in 24 hours of operation. Further, the website reports that the pendulum rod has a mass of 321 kg and a length of 4.48 m, and the bob attached to the rod has a mass of 203 kg.