[en] Measurement of the peak kilovoltage of an x-ray beam is discussed. The method involves monitoring the scattered or transmitted radiation when a sample is placed in the primary x-ray beam. The intensities are monitored over a range of tube kilovoltage around the K-edge energy of the sample. When either absorption or fluorescence is observed, it is known that the tube kilovoltage is greater than the K-edge energy for that scattering material. By using different elements, a series of calibration points can be obtained