Age, mass, extinction, and metallicity derived for samples of 10 000 artificial clusters and with true mass log ₁₀(M/M_⊙) = 4 when the metallicity is unknown. In each case, the true metallicity is indicated at the top of each column, and also by the vertical dashed line in metallicity panels (bottom row of panels). In the block of panels a), only UBVRI photometry has been used with σ = 0.05 mag of photometric errors. In block b) JHK filters have been added to UBVRI, with σ = 0.1 mag of photometric errors. In block c) GALEX filters have been added to UBVRI, with 0.15 mag of photometric errors. In metallicity panels, regions are defined around the true metallicities (shaded area ±2 bins around true metallicities). The percentage of clusters classified according to metallicity in this region is indicated. Mass and metallicity histograms are normalized so that the area below the histogram is 1.