Calculated and observed UV spectra for ζ Puppis. The observed spectrum shows the Copernicus (Morton & Underhill 1977) and IUE (Walborn et al. 1985) high-resolution observations (thin line), and the calculated spectrum (thick line) represents the standard model with respect to the stellar parameters (model D⁺ – upper panel). The calculated spectrum in the lower panel represents also the standard model, however, here a value at the upper end has been chosen for T_eff (model D⁻).