Polarisation position angle as a function of rotational phase for PSR J0437−4715 as measured with the Parkes telescope at 10 cm, 20 cm, and 50 cm (top to bottom panels). Bins with a polarisation degree Π_i < 30% have been removed. The best values for the PPA fits from the RVM are reported in Table 2. The radio pulse profile is shown in grey for better identification of the pulse. The RVM fit is shown with a solid red line.