Upper left panel: positional accuracy from MMF3 based on simulations for the SZ challenge. Upper right panel: distribution of the distance between the SZ blind position and the X-ray position (D_SZ−X) for 167 known, or confirmed with XMM-Newton, X-ray clusters. Lower panel: separation of the SZ blind and X-ray positions D_SZ−X as a function of D_SZ−X normalised to the cluster size θ_500,X.