Stellar metallicity vs. equivalent width predicted by Starburst99 models for the ten absorption lines studied in this paper. The gray squares are derived assuming a standard upper-mass cut-off of 100 M_⊙, while the blue triangles are calculated assuming a cut-off mass of 300 M_⊙. All the symbols are representative of a constant SFH and a stellar age of 100 Myr. The shaded regions allow the stellar age to vary between 50 and 100 Myr. The other details of the models are the same as in Fig. A.2.