Left: estimated SZ flux from a cylinder of aperture radius 5 × r₅₀₀ () as a function of the X-ray luminosity in an aperture of r₅₀₀ (L₅₀₀), for the 893 NORAS/REFLEX clusters. The individual clusters are barely detected. The bars give the total 1σ error. Right: Red diamonds are the weighted average signal in 4 logarithmically-spaced luminosity bins. The two high luminosity bins exhibit significant SZ cluster flux. Note that we have divided the vertical scale by 30 between Fig. left and right. The thick and thin bars give the 1σ statistical and total errors, respectively. Green triangles (shifted up by 20% with respect to diamonds for clarity) show the result of the same analysis when the fluxes of the clusters are estimated at random positions instead of true cluster positions.