Example of a BOSS quasar spectrum of redshift 2.91 The red and blue lines cover the forest region used here, 104.0 <λ_rf< 120.0. This region is sandwiched between the quasar’s Lyβ and Lyα emission lines at 400.9 and 475.4 nm The blue (green) line is the C2 (C3) continuum model, C_q(λ), and the red line is the C1 model of the product of the continuum and the mean absorption, . (See text.)