The blue polarised spectrum of WD 1105–340 observed with FORS. The scale of I is arbitrary. The meaning of symbols in the upper panel is the same as in Fig. 2. The green bars above and below the spectra show the wavelength windows included in the computation of ⟨B_z⟩. Lower left panel: correlation of Stokes V/I with the local slope of the spectral line, while the lower right panel shows the same correlation for the null spectrum N_V.