Vertical, horizontal and longitudinal displacement of three hitch points and three components of directional cosine of the hitch plane determined by right and left lower hitch points and top hitch point, which represent position and orientation of plow attached through a three points hitch system with position-controlled hydraulic device, are analytically derived concerning the two variables, using Cartesian co-ordinates fixed to a tractor. One variable is chosen as a deviated angle of lift arm m from horizontal plane and the other is angle of lateral displacement of left connecting rod or left lower link.
An example of electronic computation for Massey Ferguson FE-35 system is shown by the figures. In this example, computation is made for variable length of right connecting rod, and the depth and width deviation of plowing are shown to be restored by the change of pitch and yaw angles resulted from those devi-ations. When the reversible plow is used, rolling of plow is induced by the lateral displaceme, however, vertical displacement is nearly independent.