arrangement allows the flyman to control the speed of ascent and/or descent and provides greater safety for people on the stage below. The proper "Out/High" trim for the batten is set when the sand bag reaches the fly floor in its descent (adjustable) and the proper "In/Low" trim for the batten is established when the line set (previously tied off to the pin rail) is fully extended (adjustable). This makes it unnecessary to "spike" or "mark" either the line set or the lift line. The Hemp system relies on being slightly "batten heavy" to allow the load to travel to the floor/deck. Because the ropes are flexible there is physically no way to move/push the sandbags "Out" if the weight on both sides is equal. Another hand line, known as a jack line, may be used to lift the sandbags if they are heavier than the batten load. (UNSAFE condition) The jack line, which runs up to a loft block and back down to the trim clamp, is tied off to a belaying pin adjacent to the one used for the line sets lift lines, either at the same, or a secondary, pin rail. Pulling on the hand lines of a hemp set flies a line set out. Pulling on the jack line flies a line set in. Hemp systems can be easily configured for spot rigging, where lift lines must be frequently relocated. They are much less expensive and easier to install than counterweight fly systems, though somewhat more difficult to operate. Counterweight rigging system First introduced in Austria in 1888, counterweight rigging systems are the most common fly systems in performing arts facilities today. In a typical counterweight fly system, an arbor (carriage) is employed to balance the weight of the batten and attached loads to be flown above the stage. The arbor, which carries a variable number of metal counterweights, moves up and down vertical tracks alongside an offstage wall. In some lower-capacity fly systems, cable guide wires are used instead of tracks to guide the arbors and limit their horizontal play during vertical travel (movement). The top of the arbor is permanently suspended by several wire rope lift lines, made of galvanized steel aircraft cable (GAC). The lift lines run from the top of the arbor up to the top of the fly tower, around the head block, across the stage to evenly spaced loft blocks,