Abstract: A process for measuring a physical quantity with a random and pulse-like character, or which is transformable into pulse form is made of a measuring chain, which supplies a result relative to the quantity. An iterative mathematical simulation is carried out taking into account the random variable character of the measured phenomenon by distinguishing the behavior of the single, double, triple, etc. events in the electronic processor of the chain optimized for this purpose. During the simulation, a determination takes place of an approximate result relative to the quantity, and the simulation result is compared with the measured result. The present invention has particular utility in the measurement of the volume activity of nuclides or radioelements present in a circulating fluid, although other utilities are contemplated.