Deviations of the derived extinction curve from the LBLRTM simulation for Cerro Paranal (observed minus model). Errorbars are at the 1-sigma level. The deviation seen at about 6300 Å corresponds to the weak O₂ absorption peaking at  ~6280 Å. The dotted-dashed lines indicate the 3-sigma deviation from the best fit solution in the range 4000–6800 Å (0.007 mag  airmass^-1). The vertical segments at the bottom mark the positions of the first 7 Balmer lines.