Delay-corrected r-band flux ratio of QSO B0957+561. The 2σ measurements of B∕A are obtained in the overlapping periods between A(+420 d) and B. Here, the ⟨t_B ⟩ and ⟨B⟩ values are the epochs and fluxes of B averaged over these periods. The grey highlighted rectangles illustrate the r-band flux ratio from HST spectra in 1999−2000 (2σ confidence interval), while the rectangle with dashed sides highlights the oscillating trend from LT photometric data in 2005−2010. The top panel shows the yearly variability and the bottom panel displays the dependence of B∕A on ⟨B⟩.