First panel: simulated axisymmetric velocity field plus random noise; the disk is inclined at i = 35° and is oriented at ﹩{\phi }_{\mathrm{disk}}^{{\prime} }=77^\circ ﹩; the rotation curve adopted follows Equation (3), with V ₀ = 170 km s⁻¹ and r _t = 2″. Middle panel: model recovered using XS. Third panel: residual map, namely observed – model. Fourth panel: cumulative distribution of the residual velocities. Different percentiles are highlighted, going from 10% (V ₁₀) to 90% (V ₉₀). 1σ encloses 84% of the data, while ﹩{V}_{80}=({V}_{90}-{V}_{10})/\sin i﹩. The ratio V ₈₀/σ = 2.67, which is approximately 1.1 FWHM.