The scope of this standard concerns that part of nuclear measurement technique in which (for instance relating to probes) the number of events (especially pulses) is directly recorded. It takes into account only the statistical character of radioactive decay and pulse counting and leaves out of consideration other influences. It presumens the duration of measurement to be short compared with the halflife of radionuclides and neglects possible dead times of apparatur used. The purpose of the standard is to fix suitable characteristic values, permitting a neutral estimantion of possible detectable results of nuclear radiation and radioactivity measurements.