Uncertainty of the EBHIS–LAB column density distribution. Top panel: relative column density difference of EBHIS with respect to LAB. Bottom panel: the 68.3% (CL-1), 95.4% (Cl-2), and 99.7% (CL-3) confidence intervals from the distribution in the top panel. Because the difference between two distributions has a wider spread than the two constituents, we rescale the difference ΔN_{H i} to the equivalent standard deviation . The dashed lines represent the theoretical expectation, for the case where the error is caused by pure thermal noise, as measured in emission-line free regions, plus an additional contribution of 2.5% that represents the typical intensity calibration uncertainties.