Optical depth τ(b) in the finite-width disk model for the exponential vertical profile with the width-scales (1) h′ = 325 pc; (2) h′ = 200 pc; (3) h′ = 150 pc; (4) h′ = 100 pc; (5) h′ = 88 pc /the best fit/ (solid lines). For comparison, the thick gray line represents the τ(b) in the infinitesimally thin disk model for which the equivalent volume mass density was obtained assuming the exponential vertical profile with h′ = 325 pc. The points with error bars represent measurements data collected by several collaborations (references in the text).