the method of making a screw connection includes measuring a torque applied to the screw by a controllable screw driver device and measuring a rotation angle of the screw in individual connection steps during the making of the connection to obtain measured values of the torque and rotation angle ; calculating a change in torque over a predetermined rotation angle interval from the measured values and deriving a stiffness parameter from the change in torque divided by the rotation angle interval ; calculating a change in rotation angle over a predetermined time interval from measured values of the rotation angle and predetermined time interval and deriving a rotation speed as the rotation angle change divided by the predetermined time interval ; analyzing the stiffness parameter and the rotation speed by a fuzzy - logic device to obtain controlling output variables and operating the fuzzy - logic device in one of three operating modes to obtain the controlling output variables and to produce at least one adjusting parameter for the controllable screw driver device to accurately make the connection . the three operating modes of the fuzzy - logic device consist of three association or correlation functions for either a low stiffness mode , a normal stiffness mode and a high stiffness mode of operation or a low rotation speed mode , a normal rotation speed mode and a high rotation speed mode .