Note: The Fermi level is an absolute level to which electron kinetic energies can be accurately referenced. Historically, in Auger electron spectroscopy, the electron energies have not been referenced to the Fermi level but, instead, have been referenced to the instrument vacuum level. This level varies from instrument to instrument and does not provide a consistent reference level. However, most reported Auger electron kinetic energies have been referenced to the vacuum level, and most analysts are familiar with the variations that occur from one instrument to another for energies referenced in this way. By convention, the standard vacuum level is defined, as above, to be a consistent reference level close to the value for typical instrument vacuum levels. Energies referenced to the standard vacuum level are consistent and are within approximately \(\pu{1 eV}\) of those referenced to individual instrument vacuum levels.