Power spectra of C²(z)(1/(1 +  ⟨ x_α ⟩ ))²P_p(k) (solid line), built using simulation S1 for  ⟨ x_α ⟩  = 0.4 (z ~ 20.25). Expected error (dashed line) and expected error assuming that P_δ is known (dotted line), so the error in P_μ⁴ comes only from C(z). Dot-dashed line assumes that C(z) is known to high accuracy.