[en] Employing an earlier elaborated computer program for simulation of depositing radon decay products: ²¹⁴Po, ²¹⁴Pb, ²¹⁴Bi (²¹⁴Po) on air filter and for computing variation of their activity against time, an assessment of errors was carried out of a methods employing measurement of ²¹⁸Po + ²¹⁴Po alpha activity in three time intervals. Additionally errors of the methods measuring ²¹⁸Po + ²¹⁴Po alpha activity in three, two and one time intervals, were assessed. A few attempts were also made to measure the alpha activity in different time intervals and to assess their measuring errors. (authors). 10 refs, 4 figs, 14 tabs