Averaged 3D power spectrum compared to the expected 3D power spectrum, for 1000 realisations of the density field. The shell-averaged monopoles of this residuals in shells of width |k|−k_f/2 <  |k|< |k|+k_f/2 were then computed. The result is presented as percentage with error bars. The setting used is a sampling number per side of 256 in the top panel and 512 for the other, all in a box of size L = 1200 h⁻¹ Mpc at redshift z = 0. Both results are computed up to the Nyquist frequency.