This International Standard specifies a procedure, in the field of ionizing radiation metrology, for the calculation of the “decision threshold”, the “detection limit” and the “limits of the confidence interval” for a non-negative ionizing radiation measurand, when counting measurements with preselection of time or counts are carried out, and the measurand results from a gross count rate and a background count rate as well as from further quantities on the basis of a model of the evaluation. In particular, the measurand can be the net count rate as the difference of the gross count rate and the background count rate, or the net activity of a sample. It can also be influenced by calibration of the measuring system, by sample treatment and by other factors. This International Standard also applies, in the same way to: - counting measurements on moving objects (see B.2); - measurements with linear-scale analogue count rate measuring instruments (hereinafter called ratemeters, see B.3); - repeated counting measurements with random influences (see B.4); - counting measurements on filters during accumulation of radioactive material (see B.5); - counting spectrometric multi-channel measurements, if particular lines in the spectrum are to be considered and no adjustment calculations, for instance, an unfolding, have to be carried out (see C.2 to C.4); - counting spectrometric multi-channel measurements if evaluated by unfolding methods (see C.5), in particular, alpha- and gamma-spectrometric measurements (see C.5.5 and C.5.6, respectively).