One- and two-dimensional marginal contours of the amplitude of the count rate–mass scaling relation A_X, the intrinsic scatter around that relation σ_X, and the correlation coefficient between the WL and count rate scatter ρ_MWL, CR, labeled as ρ_WL, X for brevity in the plot. While the correlation coefficient remains unconstrained, it leads to significant degeneracies with the amplitude and scatter. Astrophysical processes like cluster age, merger state, environment, orientation, triaxiality, etc., might impact both observables and lead to selection biases. We agnostically marginalize over the entire range of such effects, thereby weakening our amplitude and scatter measurements but making the mass calibration impervious to such astrophysical effects.