For balancing flight controls on/off the aircraft, a nice document is written to understand more about this complex situation you may get into when painting an aircraft or flight control.
Update: The balance weight calculator file is updated, with more features and a better layout. Thanks to R. Meijer who made this document with lots of enhousiasm.
Direct link to the calculation file:
See the pictures for more information around the balance weighst on the rudder. A next generation rudder does not have to be removed from the a/c when it is calculated the correct way, see SRM 51-60-00.