Example for a set of diagnostic lines used in the determination of the atmospheric parameters T_eff and log g in the supergiant HD 106068 (B8 Iab), consisting of hydrogen, nitrogen and oxygen lines. The models calculated for our final parameters (red lines) are compared to observation (black lines). The same values of oxygen and nitrogen abundance are adopted for all lines, regardless of ionization stage. The ionization equilibria and the Balmer lines unaffected by the stellar wind are reproduced simultaneously. Note that various line blends of stellar, interstellar and terrestrial nature seen in the plots are exempted from the fitting process.