In obtaining the spectrum of a radioactive substance automatically, there are problems with the velocity of the voltage displacement that determines the channel with the number of counts per time unit of the integrator. By the application of very simplified assumptions on linear systems, it is shown how the sweep velocity of the voltage of the channel level and the time constant of the integrator can be selected. Formulas are given that allow the sweep velocity to be fixed as a function of the time constant of the integrator. (J.S.R.)