Left panels: normalized composition flux τ computed for the MESA cooling WD models of 0.6 (pink) and 0.9 M _⊙ (blue) using the estimation of F _X directly from the MESA output of the mass ﹩{M}_{\mathrm{core}}﹩ and radius ﹩{R}_{\mathrm{core}}﹩ of the crystallized core (dashed lines with data points), and using the analytic fit shown in Equation (4) (solid lines). Right panels: cooling tracks for the core temperature of the MESA WD models (dashed lines) along with the analytic fit done from Equation (5) (solid lines, and dotted for only the power-law component) and used to compute the analytical fit for τ. The bumps in the analytic curves are due to interpolation of the stellar parameters used to compute τ.