Emulator performance compared to the test data sets for various redshifts for the linear boost with unscreened f(R) gravity. The emulator results, along with the simulations, are given in the larger panels, while the narrower panels display the corresponding relative difference, given by B_emulator/B_simulation − 1. The grayed-out area in the same panel shows ±1%, and the Nyquist frequency of the simulations is k ≈ 5.7 h Mpc⁻¹.