a linear actuator includes a housing with a reversible dc - motor , which through a transmission can displace an activation element between two end positions , where an further switch located in the longitudinal direction of the spindle is activated and deactivated when a spindle nut passes during its travel on the spindle and provides information for a calculation model which continuously calculates the position of the spindle nut on the spindle so that the calculation model in the positions where the further switch is activated by the spindle nut is calibrated to show an absolute position which is entered as a reference point in the control .