Histograms of the ratios of the cloud mass estimates with three different methods. Left: ratio of the mass derived from the N(¹³CO) column density and that from X(¹²CO). Centre: ratio of the mass derived from the N(¹³CO) and that from the Herschel-based H₂ column density, which traces the cold dust. Right: ratio of the mass derived from X(¹²CO) and that from the Herschel-based H₂ column density.