Measuring the effectiveness of transforming the halo mass function from one density contrast to another assuming a c − M relation. Left panel: HMF at Δ₁ = 200 (dark magenta line) and Δ₂ = 500 (light magenta line) from the Uchuu halo catalogue at z = 0 against the reconstructed HMF at Δ₂ = 500 obtained for the different c − M relation models shown in the legend (see text for further information). Right panel: relative error on these reconstructions. As in Fig. 1, the shaded areas around the measured HMFs represent the statistical error on the measurement estimated as the standard deviation over 10³ bootstrap iterations.