Artificial tests for 10 000 clusters with true age and metallicity following a defined age-metallicity relation (see text), and with a true mass fixed to log ₁₀(M/M_⊙) = 4. The first column of panels displays the age derived vs. the true age, the second column shows the derived mass distribution, the third column shows the true age distribution (solid line histogram) and derived age distribution (dashed line histogram), and the last column shows the differential true age distribution (solid line), which is composed of a two-slope profile, and the derived differential age distribution (dashed line). The first row of panels shows results obtained using the UBVRI photometric system, the second row shows the results obtained using the UBVRI + JHK system and the last row shows the results obtained with the GALEX + UBVRI system. Here the metallicity of the model grid is fixed to [ M / H ] = −0.4.