A contour plot of the percent error in R _* as a function of the percent errors in ρ _* and M _*, derived in Equation (9). We see that the dependence on M _* is much weaker, and with a typical ﹩{\sigma }_{\,{\rho }_{* }}﹩ of 10%, the resulting constraint on R _* can be well below the systematic floor from evolutionary models. In the best cases, we can measure ρ _* to ∼1%, resulting in R _* uncertainties of ∼1.7%—almost entirely dominated by the systematic floor in M _*.