Residuals between SAPP parameters and reference parameters versus the signal-to-noise ratio of four stars: β Vir, η Boo, β Hyi, and α Cen A. Open circles show cases where a purely spectroscopic module (without error model) was used; these have an average and 1σ in the legend named ⟨Δ[Fe/H]⟩. Filled circles show cases where a spectroscopic module was used with the error model; these have an average and 1σ in the legend named ⟨Δ[Fe/H]_emodel⟩.