The simpliest and most convenient in a practical use method of the flow rate measurement, based on the tracer technique, is a such one, in which the passing time of the “tracer wave” is determined. The results are then obtained as a diagram of radiation intensity in the chosen points of the pipeline. The passing of the tracer over these points is marked on a recording tape in a form of the characteristic peaks. Depending on the kind of flow, the recorded peaks take the different shapes. In the first order they depend on the velocity profile in the pipe cross section. This differentiation of velocities causes that, when the distance between the detecting probe and the injecting unit increases, the tracer wave becomes more diluted, involving consequently a corresponding lengthening and flattening of peaks.