the derived variable g and the corresponding actual position value p in a step s 1 as an alternative to the actual position value p the evaluation device 16 can also accept the desired position value p the term u201c position value u201d is thus used below since depending on the application case the position value can involve the alternatives of actual value p or desired value p in a step s 2 the evaluation device 16 assigns the derived variable to the position value p and stores this pair of values in a step s 3 the evaluation device 16 checks whether it has already collected a sufficiently large number of derived variables g if the result of the test in step s 3 is positive in a step s 4 the evaluation device 16 determines on the basis of the derived variable g characteristic values of a systematic error which is contained in the actual values p and or the desired values v then in a step s 5 it deletes the previously collected derived variables g in a step s 6 the evaluation device 16 determines correction values depending on the characteristic values in a step s 7 the evaluation device 16 applies the correction values to the actual values p as already mentioned the correction values can be applied alternately to the desired values p or to the control deviation p p in the simplest case the evaluation device 16 determines the correction values.