Lever resistance (or load). It is common to call the input force "the effort" and the output force "the load" or "the resistance." This allows the identification of three classes of levers by the relative locations of the fulcrum, the resistance and the effort: These cases are described by the mnemonic "fre 123" where the fulcrum is in the middle for the 1st class lever, the "r"esistance is in the middle for the 2nd class lever, and the effort is in the middle for the 3rd class lever. The lever is a movable bar that pivots on a fulcrum attached to
Lever frame as it requires more force to move the lever. Therefore, later, especially in Germany, lever frames with pivots inside the signaller's room were used, that allow for a lever angle of approximately 180° (as seen on the photo on the right). By the movement of individual levers (or sometimes cranks), signals, points, track locks, level crossing gates or barriers and sometimes movable bridges over waterways are operated via wires and rods. The signaller chooses the correct combination of points, facing point locks and signals to operate, which will control the movement of each train through their area of control. The