Degree of polarisation P_sca by scattering on oblate dust grains as a function of the scattering angle Θ_sca and differentaxis ratio c∕b, for thetwo scattering planes perpendicular and coplanar to the grain’s symmetry axis (Θ_sca,2 = 90° and 0°, respectively). The polarisation P_ini of the incident radiation is zero and the grain size a_eff = 100 μm (left) and a_eff = 150 μm (right). The grey-shaded region indicates negative scattering polarisations, which imply a reversal of the polarisation orientation.