  We argue that the stellar velocity dispersion observed in an elliptical
galaxy is a good proxy for the halo velocity dispersion. As dark matter halos
are almost completely characterized by a single scale parameter, the stellar
velocity dispersion tells us the virial radius of the halo and the mass
contained within. This permits non-dimensionalizing of the stellar mass and
effective radius axes of the stellar mass fundamental plane by the virial
radius and halo mass, respectively.
