Computation of σ_[Fe/H] for all temperatures corresponding to log g = 3.5 dex, and all bins of [C/Fe]. The manner in which the performance of our method depends on the relative carbon abundances relates to whether or not [C/Fe] ≶ 0 dex: at and below a Solar value, σ_[Fe/H] is practically independent of carbon, but above it the uncertainty rises as carbon-enhancement increases. The last effect lessens as temperature rises. The same exercise was performed for all surface gravities of our parameter space, and the results were similar.