Upper panel: updated time series of APM 08279+5255 R-band differential magnitude with 1σ errors, adding all the photometric data available in literature (same colour code than in the upper panel of Fig. 2). Middle panel: BAL EWs computed for all the existing APM 08279+5255 spectra with 1σ errors. Lower panel: NAL EWs computed for all the existing APM 08279+5255 spectra with 1σ errors. In both middle and lower panels, Irwin et al. (1998; red triangle), Ellison et al. (1999; green cross), Hines et al. (1999; blue circle), Lewis et al. (2002; cyan square) and Saturni et al. (2015; yellow star) spectra are all included along with the Asiago and Loiano spectra (magenta dots).