Uncertainty of SSP model predictions. The upper panel shows the SSP model predicted by FASTAR for a population of 10 Gyr and solar metallicity while the bottom panel shows the associated errors. In purple, we present the uncertainty in the SSP model assuming a typical error Δlog g = 0.2 dex in the determination of the surface gravity of the stars. In red and yellow we represent the error corresponding to the metallicity (Δ[Fe/H] = 0.1 dex) and effective temperature (ΔT_eff = 0.005 dex), respectively. In grey, we show the expected total uncertainty in the SSP model.