Bottom: stellar velocity dispersion within an aperture of 10 kpc of the SDSS galaxies as a function of the inferred average log σ₁₀ given the observed values of (M_*,10, Γ_*,10), referred to in this paper as the M_*,10 − Γ_*,10 fundamental plane. Top: stellar velocity dispersion within an aperture of half the half-light radius as a function of the inferred average log σ_e2 given the observed values of (M_*, R_e), also known as the stellar mass fundamental plane. The black error bar at the bottom of each panel shows the amplitude of the inferred intrinsic scatter around each relation.