1.1 This practice describes a procedure for calibrating the electron binding-energy (BE) scale of an X-ray photoelectron spectrometer that is to be used for performing spectroscopic analysis of photoelectrons excited by unmonochromated aluminum or magnesium Ka X-rays or by monochromated aluminum Ka X-rays. 1.2 The calibration of the BE scale is recommended after the instrument is installed or modified in any substantive way. Additional checks and, if necessary, recalibrations are recommended at intervals chosen to ensure that BE measurements are statistically unlikely to be made with an uncertainty greater than a tolerance limit, specified by the analyst, based on the instrumental stability and the analyst’s needs. Information is provided by which the analyst can select an appropriate tolerance limit for the BE measurements and the frequency of calibration checks. 1.3 This practice is based on the assumption that the BE scale of the spectrometer is sufficiently close to linear to allow for calibration by measurements of reference photoelectron lines having BEs near the extremes of the working BE scale. In most commercial instruments, X-ray sources with aluminum or magnesium anodes are employed and BEs are typically measured at least over the 0–1200 eV range. This practice can be used for the BE range from 0 eV to 1040 eV. 1.4 The assumption that the BE scale is linear is checked by a measurement made with a reference photoelectron line or Auger-electron line that appears at an intermediate position. A single check is a necessary but not su