Distribution of the rms for 5000 mock catalogues (yellow histogram); here each catalogue consists of N_c randomly chosen positions on the filtered 2D-ILC map. The mean and rms of the 5000 random catalogues are 1.10 × 10⁻⁵ (shown as the black dashed vertical line) and 2.15 × 10⁻⁷, respectively. For the N_c true MCXC cluster positions, the rms is 1.17 × 10⁻⁵ (red vertical dashed line).