Difference between the observed and true metallicity, as a function of true r-band light-weighted age values at z = 0.30, considering α-enhanced simulations. Each dot is colour-coded according to σ_[zm] obtained from the posterior. The green error bars are the median and the 68% confidence interval of [Z/H] differences in bins of Age_r,true, with each bin having the same number of data points. The cyan dashed line represents the 0 value of the y-axis.