Covariance matrices of the projected gravitational potential of the cluster Abell 2142 reconstructed from its X-ray observations (Sect. 5), computed with Eq. (15). An illustration of a reconstructed potential is shown in Fig. 20, with two selected lines of cells: one in magenta, and one in green. The information on the variance in these lines is contained in the diagonal entries of the block matrices with the matching color in the present figure and in Figs. 22 and 23. The results for the HGR are shown in the top panels. Left: smoothing parameter fixed to L = 1; right: smoothing parameter linearly increasing from L = 1 to L = 10. LRG results are shown on the bottom panels. Left: smoothing parameter fixed at L = 0.2; right: smoothing parameter linearly increasing from L = 0.2 to L = 2. The same color scale has been used for the four panels, which runs from 0 (in black) to 0.004 (in white).