A contour plot of the percent error in T _eff as a function of the percent errors in R _* and F _bol, derived from Equation (11). We see that the dependence on M _* is much weaker, and with a typical ﹩{\sigma }_{{R}_{* }}﹩ of 3% and a systematic floor of L _* ∼ 2.4%, the resulting constraint on T _eff can be ∼1.5%—well below the systematic floor from evolutionary models, SED models, or spectra. In the best cases, we can measure R _* to ∼1.7% and T _eff uncertainties of just under 1%.