a method for accurately controlling a medium displacement in an inkjet printer is provided by accurately determining a relation between an actuation signal for a drive motor and a medium displacement . the method comprises the steps of establishing a set of calibration actuation signals each corresponding to a nominal calibration step and determining an achieved medium displacement step for each calibration actuation signal in the set . the set comprises at least one calibration actuation signal for actuating the drive motor to make one full revolution and at least one calibration actuation signal for actuating the drive motor to make a rotation larger than one full revolution , but smaller than two full revolutions . both a cyclic deviation and a local deviation of the nominal displacement relation is determined based on a finite series of basis functions .