Page "Fly system" Paragraph 49

The arbor's vertical position is controlled by means of a rope known as the operating line, hand line, or purchase line.

The operating line forms a loop by running from the bottom of the arbor down to and around the tension block, through the rope lock, up and over the head block and back down ( alongside the lift lines ), where it terminates at the top of the arbor.

The head and tension blocks are located above and below the full extent of the arbor's travel ( movement ), respectively, thereby enabling an operator to pull the operating line up or down to move the arbor.

When the arbor is raised via the operating line, the lift lines slacken, which causes the batten to lower under its own weight ( and the weight of its load, if any ).

Conversely, when the arbor is lowered, the lift lines increase in tension, which in turn causes the batten to rise.