Light curves obtained with all four telescopes and shifted by time delays of Δt_BA = 8.4 days, Δt_BC = 7.8 days and Δt_BD =  −6.5 days. The relative microlensing representations applied on curves A, C and D are shown as continuous curves with respect to the dashed blue line (see text). A fifth-order polynomial was used over the seven seasons to model microlensing on the quasar images C and D, while seven independent third-order polynomials were used for image A. The lower panels show residuals obtained by subtracting a simultaneous spline fit (grey) from the light curves.