The stepper function enables to compensate the electrodes wear affecting the welds quality. When the electrode diameter enlarges, the contact section area between the electrode and the workpiece increases as well and, as a consequence, the current density (Ampere/mm2) decreases. If the current is maintained at a fixed value throughout the whole electrode life, it will be noticed that the last spots are of a lower quality in comparison with the first ones. The stepper function is used in order to overcome this problem. It gradually increases the current adjustment during the welding process in comparison with the electrodes diameter enlargement: this enables to maintain a constant current density.