A variety of means of obtaining indicative velocities are listed below.
Many rotation curves are flat or even rising out to large radii.
Both planetary nebulae and globular clusters each act as point-source probes of the halo potential in Population II rich systems. Under a variety of assumptions regarding the intrinsic eccentricity of the orbits the enclosed total mass can vary more than a factor of two. Removal of physically associated but unbound pairs, interlopers, and accidental projections are problematic.