This type of counterweight flying system is commonly used where there is insufficient clear space for the necessary structural and moving components to be accommodated, this may be due to the fly tower roof structure, doorways at stage level or a desire to maintain a clear wing space.
Loading for a double purchase counterweight set is differs from single purchase; 1kg of weight applied to the scenery bar must be counter-balanced by 2kg of weight loaded into the counterweight cradle.
Similarly; 1m of vertical travel of the counterweight cradle will result in 2m of scenery bar travel.