Abstract: In order to determine whether the screwing home of a threaded element, such as a screw, by a power tool has been acceptably executed, the number of revolutions undergone by the threaded element during the screwing operation is measured as a function of time. The revolution-time function derived for the screwing operation is compared with a reference function corresponding to an acceptable screwing operation. The comparison shows up unacceptable screwing operations and can be performed both visually and by a microcomputer. Apparatus for effecting such monitoring of screwing operations includes sensing means for measuring rotation of the output shaft of the power tool and circuit means for processing the output of the sensing means and effecting the comparison with the reference function.