The center of mass to laboratory transformation and averaging over beam velocity and spatial profiles, detector slits, etc., that are necessary to compare theoretical differential cross sections directly with crossed molecular beam data are presented in easily used forms. A theoretical model is developed to accurately reduce the 11-fold integral over velocities, scattering volume and detector to a fourfold integral. Example calculations show how the model can be used to optimize machine resolution and to distinguish the damping of quantum oscillations due to machine averaging from that due to the anisotropy of molecular interactions.