Contours of cluster mass in 10¹⁵M_⊙ units (red curves) and redshift (blue curves) projected onto the observational plane defined by the filter output K_5θ500 and angular scale θ₅₀₀ = c₅₀₀θ_m. A cluster of fixed mass M₅₀₀ follows a red contour according to Eq. (16) as it moves out in redshift. Each mass contour follows the same pattern, simply displaced in amplitude. This figure shows how each point in the observational plane maps to a point in the cluster plane of (M₅₀₀,z).