Left: bin averaged SZ flux from a sphere of radius r₅₀₀ (Y₅₀₀) as a function of X-ray luminosity in a aperture of r₅₀₀ (L₅₀₀). The WMAP data (red diamonds and crosses), the SZ cluster signal expected from the X-ray based model (blue stars) and the combination of the Y₅₀₀−M₅₀₀ and L₅₀₀−M₅₀₀ relations (dash and dotted dashed lines) are given for two analyses, using respectively the intrinsic L₅₀₀−M₅₀₀ and the REXCESS L₅₀₀−M₅₀₀ relations. As expected, the data points do not change significantly from one case to the other showing that the Y₅₀₀-L₅₀₀ relation is rather insensitive to the finer details of the underlying L₅₀₀−M₅₀₀ relation. Right: ratio of data points to model for the two analysis. The points for the analysis undertaken with the intrinsic L₅₀₀−M₅₀₀ are shifted to lower luminosities by 20% for clarity.