Abstract: A nonintrusive method for determining the magnitudes and spatial and temporal origins of individual dynamic (time varying) torsion loads acting in superposition on a rotating shaft or system of shafts includes combining the measurements of said shaft's inertial response to the dynamic torsion loads with the measurements of discrete relative angular displacement parameters at causally connected space-time points. Changes in the shaft's characteristics, such as those due to change in its temperature or degradation of its structural integrity, can be monitored to provide updated torque determinations that maintain accuracy by taking these changes into account and to provide information on the onset and location of shaft fractures. Apparatus based on the method of this invention is self calibrating.