Histograms of the distribution of mass-weighted mean ages and metallicities inferred when repeating the fit 256 times; changing the parameters, the set-up, and the regularization, as described in the text. These distributions were only used to estimate the uncertainties on the values reported in Table 4. The mean ages ([M/H]) of the distributions shown here are not identical to the values found with the best possible setup (listed in the table) but do not differ by more than 1 Gyr (0.04 dex).