Distribution of fractional errors on P_lin(k, a, θ) as a function of k for the extended cosmological models considered in this work (left) and for ΛCDM (right). The bands given the 1 and 2σ values across the LH (Table 1), with the dashed lines indicating 1% error. When averaged over k, we find that our expressions have a root mean squared error of 0.28% for the extended cosmology, and 0.41% for ΛCDM.