The key component is a rocker beam that keeps the centre axis vertical at all times, even if the two supporting hoists are not running at the same speed or offset. The centre of the unit has a large main axle and friction bearing, and a manually engaged disc brake is used to hold the pan (horizontal) angle. Scales are fitted to enable users to measure or check angles, and with a SWL of 1818kg it is suitable for most speaker systems.
(James Eade)