Lever force F at a point "A" located by the coordinate vector r on the bar. The lever then exerts an output force F at the point "B" located by r. The rotation of the lever about the fulcrum "P" is defined by the rotation angle "θ" in radians. Let the coordinate vector of the point "P" that defines the fulcrum be r, and introduce the lengths which are the distances from the fulcrum to the input point "A" and to the output point "B", respectively. Now introduce the unit vectors e and e from the fulcrum to the point "A"
Lever frame or behind it. This may be accompanied by a description of the lever's function. Usually, a large track diagram is positioned within easy view of the operator, which clearly shows each lever number adjacent to symbols representing the items of equipment that they operate. Levers are commonly coloured according to the type of equipment they control, the code of colours varying between different railway administrations. For example, in British practice, the following code generally applies: a red lever controls a stop signal or shunt signal, a yellow lever controls a distant signal, a black lever controls a set of points,