Normalised and rectified, rms(squared)-weighted average spectra of the 4428 Å DIB, with overplotted Lorentzian profiles fit to the individual spectra, in (from top to bottom) the Medusa sample; the ARGUS sample; the ARGUS spectrum of the unresolved core of R 136; the UVES sample. Three sharp stellar photospheric lines that were fit simultaneously with the DIB are marked with stars (see Appendix A). Spectra were included only if reasonable fits could be obtained.