Comparison of total column density of H-nuclei N(H) derived from the DNM analysis and from observable column densities. The quantity plotted along the horizontal axis, N(H) = N(H I)|_cham + N(DNM) + 2W_CO , is thequantity fitted in the global DNM analysis and is the same in both panels. The vertical axis in each panel is the inferred total hydrogen column density N(H) = N(H I)|_cham + 2N(H₂) but calculated differently: at top, with N(H₂) = W_CO , and at bottom with N(H₂) = N(HCO⁺)∕3 × 10⁻⁹. The error bars assume ± 50% errors in W_CO and N(HCO⁺)/N(H₂).