Expected values of the extracted flux (left panel) and the estimated S/N (right panel) when an incorrect F_X/Y₅₀₀ relation is assumed. The figure shows the ratio with respect to the expected value corresponding to the true relation as a function of the relative contribution of the X-ray and SZ background noises ω (low ω values represent better SZ maps and high ω values correspond to a better X-ray map). Different values of a = (F_X/Y₅₀₀)_assumed/ (F_X/Y₅₀₀)_true are shown in different colors, according to the legend.