Abstract: A method for quality assurance of screw joint tightening results when tightening a screw joint to a needed pretension condition (FN) by means of a torque delivering power tool, wherein one or more simulation procedures of a screw joint tightening process via a specific algorithm aiming at the needed pretension condition (FN) by using programmed data relating to the screw joint geometry, expected frictional conditions, power tool characteristics, a tightening strategy and suitable tightening parameter values, thereby arriving at a simulated pretension condition (FS) which is compared to the resultant pretension condition (FP) of a practically performed tightening process performed via the same specific algorithm, and evaluating the outcome of the comparison for quality acceptance or refusal.