Determination of the regularisation weight μ by the L-curve method. The reconstructions were performed on a grid of weights (logarithmic grid of 25 values from 10⁷ to 10¹³) for the two epochs (A in red and C in blue). For each reconstruction, the values of χ² and f_prior were traced in this graph. The best value of the weight is that in the shoulder of the curves. We have chosen 10¹⁰ for both epochs.