Left panel: power spectrum bias from E − B mixing due to the miscalibration of the absolute polarisation angle. This bias is plotted for the different absolute calibration errors Δψ_Gal presented in Sect. 2 (from red to blue, see legend). The Planck Collaboration XIII (2016)ΛCDM best-fit primordial tensor model for r = 10⁻³ and r = 10⁻⁴ (solid and dashed black lines, respectively) and lensing model (grey line) are also displayed. Right panel: same as the left panel, but relative to the primordial tensor model for r = 10⁻³.