Standard spatial and velocity Cartesian coordinates for a model CV. The C.O.M. of the binary is marked with a plus (+) while that of the primary and secondary are marked with crosses (×). Overlays of the Roche lobe of the primary (dashed line), the accretion stream (solid line) from the secondary towards the primary (up to an azimuth angle of 30°), as well as radii at decrements of 0.25 times the outer disc radius are shown (red dashed circles). The outer disc radius is the 3:1 resonance radius while the inner disc radius is based on an absolute radial velocity of 1800 km s^-1. There are also two arbitrary reference points, A and B, shown in the disc.