Evolution of polarization parameters of B_0017+8135_82, which is found to be variable. (a, b) Evolution of the relative Stokes parameters. The dashed black line shows the weighted average; the red dashed lines show the corresponding 1 σ uncertainty. (c) Distribution of measurements on the relative Stokes parameters plane. (d, e) Evolution of the polarization degree and the electric vector position angle. The dashed black line shows the weighted average; the red dashed lines show the corresponding 1σ uncertainty. (f) EDF of measured polarization in both bands together with expected CDF of polarization measurements for a constant source with similar uncertainties.