A calibrated measuring system for customer-specific tool holders and special applications in machine parts. Together with a rotor and a stator, the DDU-4 measuring transducer constitutes a sensor system for contactless monitoring of rotating and rigid tool holders. The measuring principle of the cylindrical DDU rotor is based on strain gauge technology. Strain gauges are attached to the tool holder and are firmly connected to it. The rotor continuously measures torque and axial force values simultaneously. Preprocessing of measurement data and tool-breakage monitoring is carried out in the measuring transducer.