problem of follow-up control. One example for follow-up control is keeping a ship on course (e.g. when manoeuvring through a narrow channel). Depending on the path of the channel, the setpoint or desired value w is continuously moving (see the following diagram). By changing the position of the rudder (manipulated variable y), the controller R exerts influence on the actual angle of the ship's course, i.e. the controlled variable x, and thus acts to continuously adjust it to the set course so that the deviation between the setpoint or set course and the actual course (error signal e) becomes as close to zero as possible. Disturbances, e.g. wind or water currents also arise and must be accounted for.