Light curves of blazar 3C 454.3. From the top, the first panel shows the γ-ray photon flux for photon energies above 100 MeV obtained from the Fermi LAT data in 10-day bins; the second panel shows the optical continuum at source-frame 3000 Å, obtained independently using two analysis methods (spectral decomposition, blue circles; simplified power-law fit, red/grey crosses); the third panel shows the corresponding values of the spectral index α such that f_λ ∝ λ^α; the fourth panel shows estimates of the spectrally integrated Mg II line flux, either separated from the Fe II continuum (decomposition method) or not (simplified method); the fifth panel shows the source-frame FWHM width of Mg II line obtained in the decomposition method and corrected for instrumental broadening; the sixth panel shows the rms of continuum subtracted spectra calculated over the continuum fitting spectral windows, with the limiting value of 7 × 10⁻¹⁷ erg s⁻¹ cm⁻² Å⁻¹ indicated with the dashed line. Results reported in León-Tavares et al. (2013; Steward) and Isler et al. (2013; SMARTS) are indicated in the second and fourth panels. Periods of interest for spectral stacking are marked with vertical stripes or lines.