Comparison of the probability density distributions of the convergence ratios f_κ and reduced shear components g_i, i = 1, 2 of the SIE lens at the centres of light of the four multiple images of the second source with their true values (red lines). The dark grey shaded area, the grey shaded area, and the light grey shaded area delimit the 1-, 2-, and 3-σ confidence intervals, respectively.