Sanity check employing GCs (from Miocchi et al. 2013), thought to be self-gravitating systems. Top panel: Fit to one of them, NGC 288. Middle panel: Diagnostic diagram for NGC 288 inferred from the above fit. Because it is self-gravitating, the parameters of the stellar distribution (indicated by the star symbol) are those of the true gravitational potential (r_sp and c_p), and they appear in the allowed region of the diagnostic diagram. Bottom panel: Diagnostic diagrams combining all GCs together. As in the middle panel, the star symbols indicated the true potentials, and they all fall well within the allowed region in the diagnostic plot.