A special kind of transducer making it possible to measure normal and tangential contact stresses during rolling has been developed. As normal stresses are approximately ten times larger than the tangential, and since cross signals must occur, a proper calibration of the sensor is essential. Calibration must consist of a number of simultaneous applications of known normal and tangential loads. This problem was solved with an especially designed apparatus called Surface Loader (SL). The design makes it possible to apply a force of known value and direction to a small area of the surface. If the value and direction of force is known it might be treated as applying normal and tangential load using the force components. The contact end of the force actuator has a low carbon steel nose, making it possible to reach high friction coefficients. A precise determination of the applied force direction is possible by the invented method of loading. It is applied by a special construction of SL, controlling of the bending moment acting on the actuator by measuring the reaction force and using a special loading procedure: (i) Applying normal force on the sensor surface - a lateral support is used, (ii) Removing the lateral support, (iii) Developing friction by horizontally moving the platform until the moment in the actuator disappears. © 2011 IBF (RWTH Aachen) & IUL (TU Dortmund).