This document specifies a calibration procedure of the energy step and the energy scale for electron energy loss spectroscopy in (scanning) transmission electron microscopes to an uncertainty of ±3 % for the energy range 0 eV to 3 000 eV. This document is intended for electron energy loss spectroscopy with transmitted electrons through sufficiently electron transparent samples, such as a thin foil sample, and is not designed for backscattered electrons from a bulk sample.