Binned spectra at sidereal phases ϕ = 0.2–0.3 (blue) and 0.7–0.8 (red) for epochs 1992 (left) and 1995 (right), showing their very similar phase-dependent line profile variability. The abscissa is in velocity units centered on the reference wavelengths: top: N V λ1238.32; middle: C IV λ1538.20; bottom: N IV λ1718.55. The corresponding wavelength bands defined for these features and listed in Table 2 are indicated in the left panel with horizontal lines.