Left: E(B−V)∕N_HI (top), E(B−V)∕N_H with the f_c(T_D) correction Eq. (7) (middle), and E(B−V)∕N_Htot including a correction for X_CO = 4.0 × 10²⁰ cm⁻² (K km s⁻¹)⁻¹ (bottom). Units are 10⁻²² cm² mag, displayed are data around the mean within a 2σ range on both sides. For a comparison of E(B−V)∕N_HI after restricting the data to the canonical thin gas and to CO–bright regions we refer to Fig. 1. Right: τ₃₅₃ ∕N_HI (top), τ₃₅₃∕N_H (middle), and τ₃₅₃∕N_Htot (bottom). Units are 10⁻²⁷ cm², also displayed are data within 2σ around the mean.