Influence of the error ΔP of the stellar rotation period P on the squared amplitudes of the first and second harmonics of rotational modulation of F (the analyzed parameters in our method). The variable is the average ratio between the values calculated for the same stellar rotation but using the adopted P and slightly modified P + ΔP rotation periods. The individual ratios were averaged using the whole stellar set (513 objects) for both harmonics with numbers m = 1 (squares and solid line) and m = 2 (diamonds and dashed line).