Various realizations of the numerical simulation of the intervelocity deprojection (sample of 13 000 pairs). Left figure: an example of a single realization. The original 3D velocities have a Gaussian distribution of standard deviation σ_v = 90 km s⁻¹ and peak velocity 190 km s⁻¹ (cutoff on V = 0) [red curve]. We randomly projected a random realization of this Gaussian distribution, then deprojected it using the constant bin method with a bin width 20 km s⁻¹ (see text). The blue broken line is the obtained deprojection, compared with the ± 1σ lines estimated from 100 realizations (see Fig. 6). Right figure: various realizations using differences on non-adjacent bins (), for the same original velocity PDF. We randomly projected random realizations of this Gaussian distribution, then deprojected it using the constant bin method (blue histograms) with a bin width 20 km s⁻¹ (see text). The dashed orange lines show the ± 1σ lines estimated from 100 realizations. The quality of the deprojection is improved by a factor of ≈ 2 with respect to the adjacent bin method.