Methods are disclosed for calibrating a force constant of a movable stage. In an exemplary method, in first and second preliminary pre-stepping motions of the stage, a baseline force and a calibration force, respectively, as exerted by the stage are measured. From a force-variation ratio of the baseline force and calibration force an inverse closed loop factor is estimated. In at least one subsequent pre-stepping motion of the stage before a respective use of the stage for holding an object, a residual force-variation ratio is estimated, a force-compensation factor is updated from the residual force-variation ratio, and a respective force-variation coefficient is determined from the force-compensation factor.