Age metallicity relation for a simulated exponential star formation history with different τ and with two different chemical evolution models. Solid lines indicate the simulated age-metallicity relation whilst the points show the recovered values. Open symbols shows the recovered age-metallicity relation in the case of constant metallicity with age whilst the filled symbols show the recovered age-metallicity relation in the case where the metallicity increase with time. Error bars represent the rms dispersion of a set of 50 Monte Carlo simulations where each pixel is moved according to a Gaussian distribution of width given by the errors. The synthetic spectra have been degraded to the resolution of the data and noise have been added to simulate a S/N per Å of 40.