Method of obtaining a high clamp force accuracy at a threaded joint mounting process performed by means of a hand held torque delivering power tool including a housing, and a motor driven output shaft rotatably supported in the housing about a rotation axis, comprising the following steps: • registering during a certain interval (φ 1 - φ 2) of a threaded joint mounting process a tightening torque applied on the joint, the rotational movement of the output shaft relative to the housing, and occurring angular displacements of the housing about the rotation axis and in relation to an immobile point, • registering during a certain interval (φ 1 - φ 2) of a threaded joint mounting process a loosening torque applied on the joint, the rotational movement of the output shaft relative to the housing and, occurring angular displacements of the housing about the rotation axis and in relation to an immobile point, • calculating the true rotational movements of the output shaft relative to an immobile point by comparing the rotational movement of the output shaft relative to the housing with registered occurring angular displacements of the housing about the rotation axis and in relation to an immobile point, • comparing the applied tightening torque during said certain interval (φ 1 - φ 2) with the applied loosening torque during said certain interval (φ 1 - φ 2) to thereby determine the clamp force related tightening torque, • relating the determined clamp force related tightening torque to the calculated rotational movement of the output shaft relative to an immobile point to determine the clamp force coefficient of the threaded joint, and • completing the threaded joint mounting process by tightening the threaded joint to a target clamp force level (F T) by applying a torque based on the determined clamp force coefficient. • registering during a certain interval (φ 1 - φ 2) of a threaded joint mounting process a tightening torque applied on the joint, the rotational movement of the output shaft relative to the housing, and occurring angular displacements of the housing about the rotation axis and in relation to an immobile point, • registering during a certain interval (φ 1 - φ 2) of a threaded joint mounting process a loosening torque applied on the joint, the rotational movement of the output shaft relative to the housing and, occurring angular displacements of the housing about the rotation axis and in relation to an immobile point, • calculating the true rotational movements of the output shaft relative to an immobile point by comparing the rotational movement of the output shaft relative to the housing with registered occurring angular displacements of the housing about the rotation axis and in relation to an immobile point, • comparing the applied tightening torque during said certain interval (φ 1 - φ 2) with the applied loosening torque during said certain interval (φ 1 - φ 2) to thereby determine the clamp force related tightening torque, • relating the determined clamp force related tightening torque to the calculated rotational movement of the output shaft relative to an immobile point to determine the clamp force coefficient of the threaded joint, and • completing the threaded joint mounting process by tightening the threaded joint to a target clamp force level (F T) by applying a torque based on the determined clamp force coefficient.