Method for the documented tightening or retightening of a screw connection consisting of a threaded bolt and a nut screwed onto the threaded bolt and supported against a support, by using an axially operating tensioning device comprising a cylinder housing, an exchangeable bush which is arranged in the cylinder housing and at the end thereof facing the threaded bolt is provided with an internal thread and able to be screwed onto the threaded bolt, and at least one piston which is able to be moved axially in the cylinder housing and able to be impinged with hydraulic pressure and by way of which the exchangeable bush is axially entrainable, and further using a rotary drive for the nut, which is attachable as a module externally to the cylinder housing, and a process control unit provided with a documentation module, wherein the method comprises the following steps: a) tightening the nut by means of the rotary drive with a tightening torque which is at least required for the nut to bear on the support without a gap; b) longitudinally elongating the screw connection by activating the tensioning device by exerting axial tension on the thread end of the threaded bolt that protrudes beyond the nut; c) further tightening the nut by means of the rotary drive while maintaining the longitudinal elongation, detecting a rotation angle covered during this further tightening by means of a rotation angle sensor in the process; d) computing the lengthening of the threaded bolt associated with the longitudinal elongation from - the rotation angle covered and - the thread geometry of the screw connection; e) computing a longitudinal force in the threaded bolt from - the lengthening, - the bolt diameter and - the bolt length; characterized in that the computed longitudinal force, conjointly with an identifier identifying the screw connection, is stored in the documentation module, in that the tightening and the further tightening of the nut is carried out with the same tightening torque while exerting a force by means of a hand tool attachable to the rotary drive, in that the torque used when tightening and when further tightening the nut is detected by means of a torque sensor and a corresponding torque value is stored in the documentation module, and in that detecting the torque takes place when tightening and further tightening the nut in the module. a) tightening the nut by means of the rotary drive with a tightening torque which is at least required for the nut to bear on the support without a gap; b) longitudinally elongating the screw connection by activating the tensioning device by exerting axial tension on the thread end of the threaded bolt that protrudes beyond the nut; c) further tightening the nut by means of the rotary drive while maintaining the longitudinal elongation, detecting a rotation angle covered during this further tightening by means of a rotation angle sensor in the process; d) computing the lengthening of the threaded bolt associated with the longitudinal elongation from - the rotation angle covered and - the thread geometry of the screw connection; - the rotation angle covered and - the thread geometry of the screw connection; e) computing a longitudinal force in the threaded bolt from - the lengthening, - the bolt diameter and - the bolt length; - the lengthening, - the bolt diameter and - the bolt length;