Richness estimator tests using Abell clusters with spectroscopic redshifts. Panel (a) shows our richness measure using the spectroscopic redshift from SR99 compared with the richness using our photo‐z. Panel (b) is the ratio of richnesses using 1.5 and 1 Mpc radii. Panel (c) shows our richness (using z_spec) against Abell’s. Panel (d) compares Abell’s richness with our measurement using the Kim (2001) technique to count galaxies with m₃ < m < m₃ + 2. In the bottom panels, each small dot is a single cluster, with the large squares representing binned data.