Marginal (panels on the diagonal) and joint (other panels) probability distributions of the mass-richness scaling derived from real and simulated data for a PS1+Euclid-like survey. Red jagged contours and histograms refer to probabilities computed from the MCMC sampling, while the blue smooth contours/lines refer to a Gaussian approximation of the numerically found posterior. Contours are at 68% probability level. Vertical (cyan) lines and crosses indicate the values used to generate the data, while the dashed (green) lines show the current low-redshift calibration of the richness-mass scaling.