There an interesting thing about adjusting the clock by adding/subtracting pennies to the pendulum of the clock.
Those who've studied the physics of pendulums might remember that the mass of a pendulum doesn't affect the period of a pendulum.
So how does adding or removing a penny to the pendulum of the clock have any effect on it?
It's because the penny is added/removed above the centre of mass, so adding a penny raises the centre of mass, and speeds the clock up, while removing a penny does the reverse.