Abstract: An apparatus for feedback adjusting the working condition of a working machine on the basis of measured dimensions of processed workpieces, including a determining device for determining automatic and manual compensating values, and an applying device for applying the automatic and manual compensating values (Ui, U') to a machine controller for adjusting the machine working condition. The determining device determines the automatic compensating value on the basis of first or second estimated dimensional values of the workpieces obtained in an automatic compensating cycle. Each first estimated dimensional value is a sum of an actually measured dimension (X) of the workpiece and a last compensating value (U'), while each second estimated dimensional value is a sum of the actually measured dimension, the last compensating value and a previous compensating value (Ui-2, Ui-1) preceding the last compensating value. Also disclosed is a method of feedback adjusting the machine working condition.