A pile of old coins which have helped keep the clock mechanism of London's Big Ben accurate for the last 150-years were replaced Thursday by a new five pound ($8.29) coin to mark the 2012 Olympics. The pre-decimal pennies are stacked on the pendulum of the clock and have acted as weights to help regulate it since 1859 when the clock tower was completed and the first strikes of its 13.7 ton bell, nicknamed “Big Ben,” were heard. Adding or taking away coins effects the pendulum's center of mass and the rate at which it swings, said Mike McCann, the clock's keeper. Adding one penny causes the clock to gain two-fifths of a second in 24 hours. The new coins have been produced as part of the Royal Mint's collection to celebrate the London 2012 Olympics - which features Big Ben's clock face.
