Posterior distributions for Y_tot, θ_s and α for simulated low-noise data, for clusters with θ_s = 1.8 (top), 4.5 (centre) and 7.4 (bottom) arcmin and universal (γ,α,β), with the two-dimensional prior on Y_tot and θ_s and a uniform prior on α between 0.1 and 3.0 (β fixed to the correct, input value). The input values are indicated by red triangles, and the posterior means with green crosses. θ_s is in arcmin and Y_tot is in arcmin².