While many people refer to the clock tower of the Palace of Westminster as 'Big Ben,' that name technically refers only to the largest of the five bells inside. The tower itself was renamed the Elizabeth Tower in 2012 to honor Queen Elizabeth II's Diamond Jubilee. Completed in 1859, the clock is famous for its accuracy and its Victorian Gothic design by Augustus Pugin. Each of the four clock faces is 7 meters in diameter and contains 312 pieces of opal glass. A unique tradition involves using old British pennies to adjust the clock's time; adding or removing a single penny from the pendulum can change the clock's speed by 0.4 seconds per day. The Great Bell (Big Ben) weighs 13.7 tonnes and has a distinctive crack, which occurred shortly after it was installed, giving the bell its unique tone.