Relation for cluster line-of-sight velocity dispersion σ and richness λ_norm. The black data points are for all clusters in our analyzed catalogs (see Table 4) apart from the blind-mode runs. In total, 1699 clusters with N_members ≥ 15 spectroscopic members were selected. The red line is the best fit to the data, and the light red shades show the uncertainty of the relation. The observed scatter δ_obs,orth (orange) was measured orthogonal to the best-fit relation in 9 bins. The median orthogonal component of the measurement uncertainties δ_m,orth is shown for each bin in blue. By subtracting δ_m,orth from δ_obs,orth in quadrature, we estimated the intrinsic scatter δ_in for each bin. It is shown in green.