Comparison between $N_{\mathrm{H}}^X$ and $N_{\mathrm{H}}^{21\mathrm{c}\mathrm{m}}$ measurements. Top panel: comparison between the $N_{\mathrm{H}}^X$ values obtained from the best fits and the $N_{\mathrm{H}}^{21\mathrm{c}\mathrm{m}}$ measured in the lines of sight. The log($N_{\mathrm{H}}^X$)/log($N_{\mathrm{H}}^{21\mathrm{c}\mathrm{m}}$) = 1 ratio is plotted with a solid blue line. The data has been rebinned for illustrative purposes. Bottom panel: same as the top panel but including only high-latitude sources (|b| > 75°, red color) and low-latitude sources (|b| < 15°, blue color).