Abstract: A system employing structural moment detectors for collecting and interpreting data reflecting the effect of at least a selected one of a plurality of forces acting on a structure such as a machine tool. The output signals from the moment detectors are processed to modify the information content (including rejecting components of the signals which reflect extraneous forces other than the selected one). The processed signals are then manipulated to provide secondary signals which are responsive to the condition of the structure as a result of the application of the selected force.