Position angle of the linear polarization as a function of pulse phase, for PSRs J0613−0200, J1022+1001, J1024−0719, J1600−3053, J1643−1224, and J1713+0747. The position angles, Ψ, were calculated using the Q and U Stokes parameters plotted in Figs. 3–6, as Ψ = arctan . Results from NUPPI observations calibrated with the SINGLEAXIS method are represented as orange squares. Those obtained with the improved calibration scheme are shown as green circles. Reference results from Dai et al. (2015) are shown as blue crosses. For each pulsar, the pulse profile is shown in light gray for reference.