Top left panel: polarization degree map p, uncorrected for noise bias, of the Crab nebula. Top right panel: noise bias corrected p values as a function of total intensity map (Stokes I). The condition I_pol > 5 is satisfied for those values. Bottom left panel: polarization angle map ψ (equatorial coordinates system) of the Crab nebula. Bottom right panel: distribution of ψ values represented as a function of the total intensity in the case of very high S/N where I_pol > 5. The cyan dots represent the uncertainties calculated as the dispersion between different observational scans. The black cross marks the pulsar position on the maps.