Start by creating the Actor subclasses needed for the project (the rocker arm and pan classes). If you want the weight balance to tilt gradually to any new setting (or settle into the new setting by swaying back and forth over what will be the new setting), then you may require a smooth rotating system. The class for the rocker arm should keep a reference to the two pans attached to it so it can easily acquire the weight values and determine what rotational forces that need applied. A slight drag factor should also be implemented to create the settling on a new value. This was just to give you an idea of where to start and what may be involved.