Comparison of the LSD (dashed line) and NDD (dash-dotted line) description of blended lines with the detailed radiative transfer (RT) calculation (solid line). a) Two identical unresolved lines with overlapping absorption coefficients. b) Two resolved lines that overlap because of the rotational broadening corresponding to v_esini = 10 km s^-1. c) Same as b), but the overlap is caused by the Gaussian instrumental broadening with FHWM = 0.17 Å.