Illustration of the posterior probability contours in the Y_5R500–θ_s plane for a cluster detected by Planck. The contours show the 68, 95 and 99% confidence levels. The red continuous line shows the ridge line of the contours, while the dashed lines are the ± 1σ probability value at each θ_S. The cyan line is the expected relation from Arnaud et al. (in prep.) at a given redshift.