The general inability of optical observations of low mass interacting binaries to provide accurate radial velocity measures for the stellar components is a problem for which there is no universally applicable solution. Velocity measurements are handicapped because the accretion disc about the primary often dominates the optical spectrum. Therefore spectroscopists resort to measuring line profile symmetry in individual spectra of the accretion disc in order to provide information on the primary’s motion. However, discs are not axisymmetric structures and the standard approach generally fails because the asymmetry-free inner disc emission is usually dominated by statistical noise.