I spoke with Jeffrey Mei (NYUAD) early in the morning (my time) to discuss his continuum-normalized SDSS spectra of standard stars. We are trying to look for absorption in the spectra that is associated with interstellar medium by regressing the spectra against the Galactic reddening. This is a great project, but has many complicated issues. Not the least is that it is easy to shift the spectra to the stellar rest frame, or even the Solar System barycentric rest frame, but it is hard to shift them to the mean (line-of-sight) interstellar-medium rest frame. I have some ideas, or we could look for blurry features, blurred by the interstellar velocity differences. Maybe Na D will save us?