Mapping between the fit quality metric ﹩\bar{d}﹩ and the fractional mass error δ = ∣(M_true − M_fit)/M_true∣. At the ﹩\bar{d}﹩ attained by 10 representative element sets (Fe-Peak, Low, Low+Ni, Even-Z, Mid, Mid+, Mid+N−O−K, High, High+, and All), scatter points show all δ values across the HW10 grid (16,800 models × 100 mocks =1.68 × 10⁶ points per set). Symbols mark the 50th, 68th, 75th, and 90th percentile thresholds at each ﹩\bar{d}﹩, and the smooth curves are exponential fits to these thresholds. The 75th percentile curve is highlighted (thicker line) since it is used to compute δ₇₅ in Figure 6.