FASTAR versus MILES SSP predictions. Each row shows the dependence of a specific line-strength index with age (left), metallicity (middle) and IMF slope (right, under a bimodal parameterization) for FASTAR (in blue) and MILES (orange) SSP models. In each column, the value of the assumed age, metallicity and IMF slope is indicated in the first row (corresponding to the CaHK feature). Equivalent widths are calculated at the 2.51 Å nominal resolution of both sets of models.