Ratio of the matter power spectrum (top row) and the cross-correlation (bottom row) with respect to the reference simulation, for COLA (left column) and COCA (right column) simulations with varying numbers of force evaluations, n_f. The coloured lines represent the mean over the test set. In the COCA column, the top panel of each row is plotted on the same scale as COLA, while the lower panel provides a zoomed-in version. The grey band indicates 1% agreement with the reference. COCA simulations are much closer to the reference even when using far fewer force evaluations, and the agreement improves as n_f increases.