Examples of different masks used to select the diagnostic lines. Each of the four panels shows the same wavelength range including the He II λ4542 Å line and the Si III λλ4553,4568,4575 Å triplet. The two panels on the left compare two stars of similar temperature but different υ sin i: HD 14 302 with υ sin i ≈ 65 km s⁻¹ (top left), and HD 197 460 with υ sin i ≈ 200 km s⁻¹ (bottom left). The two panels on the right compare two stars of similar υ sin i but very different T_eff : HD 24 432 with T_eff = 15 kK (top right) and HD 190991 with T_eff =32kK (bottom right). The wavelength ranges selected for each analysis are shaded in green. The masked (not used) regions are shaded in red.