ISO 20411:2018 specifies a method for determining the maximum count rate for an acceptable limit of divergence from linearity of the intensity scale in pulse counting magnetic sector-type secondary ion mass spectrometers or quadrupole secondary ion mass spectrometers. It uses a test based on depth profile analysis of two isotopes in a reference material which has a gradual concentration change between low and high concentration regimes. It also includes a correction method for saturated intensity caused by the dead time of the detector. The correction can increase the intensity range for 95 % linearity so that a higher maximum count rate can be employed for those spectrometers for which the relevant correction equations have been shown to be valid.ISO 20411:2018 does not apply to time of flight mass spectrometers.ISO 20411:2018 is only applicable to elements with minor isotopes. It is not applicable if the element is monoisotopic or contains isotopes with equal abundances.