Mass-to-richness scaling relation, M₅₀₀–R_L^⋆, for the 444 MCXC clusters included in the WHL12 catalogue (Wen et al. 2012). The best-fit relation, from BCES fit, is given by the solid blue line. We adopted 15% uncertainties on the MCXC masses as prescribed in Piffaretti et al. (2011). As no uncertainty is provided for the WHL12’s richness, we arbitrarily assumed a 20% uncertainty for all richness values. The blue shaded area shows the associated errors on the best-fit, while the dashed line marks the intrinsic scatter.