Examples of Mg II (dark-red spectrum and orange best-fit profile) and C IV (black spectrum and gray profile) absorbers matched in velocity space. The redshift of the C IV component with the largest column density corresponds to Δv = 0 km s⁻¹. We show in the upper panel the case $\mathrm{\Delta }{v}_{90}^{\mathrm{C}\mathrm{I}\mathrm{V}}\approx \mathrm{\Delta }{v}_{90}^{\mathrm{Mg}\mathrm{I}\mathrm{I}}$ (matched system) and in the lower panel the case $\mathrm{\Delta }{v}_{90}^{\mathrm{C}\mathrm{I}\mathrm{V}}>2\times \mathrm{\Delta }{v}_{90}^{\mathrm{Mg}\mathrm{I}\mathrm{I}}$ with only a partial alignment between the two ions (mis-matched system). The sightline, redshifts and measure of the velocity width are reported in the figures.