Grandfather clocks have a pendulum within them that sometimes tend to be really annoying to just here it tick back and forth repetitively. They need a long casing to hold the pendulum swings. It swings to keep track of time. The escapement in the clock controls the movement of the wheel in order to provide precisely timed impulse to keep it swinging (the source of the annoying ticking). The pendulum swings vary depending on the length of the rod. If you're one of those people who like the clock to be 5 minutes faster you simply lift the rod higher. Moving the rod up reduces the length of the pendulum, which in return reduces the pendulum's period so the clock gains time. (learned from searching
pendulum clock in youtube)
