[en] The study of the interactions of pions with helium-3 and helium-4 nuclei as well as the study of the pion-deuterium and pion-tritium interactions can give interesting results concerning the many nucleon systems, the existence of any resonant states, the value of the pion formfactor, the coupling constant (π³He³H) value and so on. Relying on these considerations we undertook during last years a study of the elastic scattering of the positive and negative pions on helium-3 and helium-4 nuclei in the energy range from 68 to 208 MeV. The study has been done by using a streamer chamber filled with helium gas at a pressure of 4 atmospheres. The elastic differential cross section data obtained by us, though on a rather small statistics, have the advantage of covering a wide range in energy, both for π⁺ and π^- interactions on helium-3 and helium-4, using the same experimental method, fact which gave the possibility of a coherent analysis of the results. Data on pion-helium-3 elastic scattering are the first experimental results of that kind obtained up to now. In this work we describe the method used in processing the experimental data in order to establish the possible systematic errors of the final djstributions. (author)