Effect of random noise with σ = 2 × 10^-4 on the Stokes V (upper panel) and CSV profiles with W_I (middle panel) and 1−ℛ_I (bottom panel) normalisations. The thick double line shows the noise-free calculations corresponding to the rotational phase 0.125 of the model Stokes profiles discussed in Sect. 2.1. The thin lines represent profiles for different noise realisations. The and profiles are obtained with the forward integration according to Eq. (14).