Spindles of machine tools are subjected to high mechanical load. This load results in thermal expansion of the spindles. The associated change in length causes a certain positioning error for the work to be performed. The SSW sensor is directly integrated in the spindle and measures the thermal expansion there of the tool holder without contact. The miniaturized eddy current sensor can also be used again immediately after a tool change. The measured value is transmitted to the CNC controller as a set offset.