From VPA Wiki
Counterweight systems are rigging systems typically found in large performing arts theaters allowing a series of rails above the stage to be raised and lowered.
- Fly systems are used to move scenery, through the utilization of pulleys and the grid system on stage. There are three main types of systems that are generally used: The Counterweight system, The Rope-Set Systems and The Motorized Flying System.
- The counterweight system is based off cables instead of using ropes to move the scenery. The cables run through loft blocks and a head block. These blocks serve as the pulleys to allow adjustment in direction of travel. Loft blocks are the grooved pulleys located on the top of a grid while the head block is a multisheave block with multiple pulleys for supporting the batten. 
- The blocks are supported on the grid above the stage. Grids are an essential part of any fly system. They are the key part to the Fly Loft. Grids are composed of system of steel I beams that support the entire system.
- The cables are tied to the counterweight arbor. A counterweight arbor is a cradle designed to hold the weights of the system. The arbor itself is designed to counterweight and balance the scenery attached to the batten. The arbor is adjusted with the height of the scenery. When the scenery is lowered to stage level, the arbor is shifted to the loading platform. The loading platform is a suspended walkway located just under the grid. When the scene is at stage level, weights can be loaded onto the arbor to balance the scenery safely.[Gillette, Michael. Theatrical Design and Production. McGraw-Hill Companies. (2008)]
- The counterweight fly system is controlled by manila rope that runs through the arbor, a head block, through a rope lock and a tension pulley. This then goes through the bottom of the arbor. The system of pulleys allows for easier changes in adjusting the batten height. The rope lock is an essential part of the system. This holds the position of the ropes keeping the system in place. While it is an convenient part of the system, it is a bulky set-up and takes up otherwise useful space. This problem can be solved through a multi-speed counterweight. This involves the locking rail positioned above the floor allowing a 2:1 ration between the position of the batten and the arbor. However, twice as much weight needs to be loaded into the arbor in order for this to work properly.
- The stage must be clear under the loading platform when loading and unloading weights in the arbor
- Do not stack counterweights where their stability is questionable
- Empty pockets when on loading platform and grid. Objects have the potential to fall and are considered dangerous to anyone below
- Inspect hardware and other equipment for wear.
- Use bolts to support hardware in systems instead of screws or nails that will wear out.
- Attach scenery before loading weights
- Unload counterweights before removing scenery
- If the scenery is lighter, the batten should be attached to the bottom of the flat.
- Inspections are essential to make sure all equipment is safe for use.
- [Gillette, Michael. Theatrical Design and Production. McGraw-Hill Companies. (2008)]