SEDs of the z ≃ 3 quasars in the rest-frame ν − νL(ν) logarithmic plane. The red circles mark all the available photometry from the SDSS-DR14 catalogue, but only the ones highlighted with black circles were used to construct the SEDs. The dashed cyan lines represent the slopes Γ₁ and Γ₂ in the 0.3−1 μm and 1450−3000 Å range (rest frame), respectively. The composite SDSS radio-quiet quasar spectrum from Shang et al. (2011) is also shown for reference with the dashed black line, normalised at 2500 Å (indicated by the dashed red line). We included the X-ray data with blue points for the soft and the hard band. The dot-dashed blue line locates the 2 keV point.