Hey Jay,
The machine is in a way simular to a tire balancer but with a strobe light. As the 2 wheels and shaft are spun it measures the imbalance and allows you to add putty to the wheel on the opposite side of the imbalance. By adding or subtracting putty, you can fine tune the wheels. Once the tech is happy with the balance he judges how much metal to be ground off and were. After removal the process is done again to make sure it is balanced.