Angles, θ, of the host stars’ relative velocities in the LISM as a function of the debris discs PAs. The dashed lines show the points where the difference between θ and PA is 90° for a disc with positive inclinations, and the dotted lines display the equivalent relation for discs with a negative inclination. This broad correlations have been extracted from the simulations made by Maness et al. (2009) when the ISM flow is on the same plane as the disc.