Results from the parameter recovery of mock Heavy Metal spectra. We show systematic offsets in the stellar population fitting code as a function of S/N for four key parameters. At each S/N, we generate 20 mock spectra and fit their elemental abundances and ages following the procedure in Section 2. The black rectangles represent the median offset between the simulated and best-fit values for the 20 realizations. The blue error bars represent the 16th and 84th percentiles of the best-fit values for the 20 realizations. The red error bars show the typical uncertainties on a single realization. The gray tick marks at the bottom of each panel show the true S/N of the individual Heavy Metal spectra. For the typical Heavy Metal galaxy, the systematic offsets are ≈−0.05 dex for [Fe/H] and [Mg/Fe] and ≈0.05 dex for log Age.