Structure functions in the observed frame, of the best estimate of intrinsic variability of the source quasars (in black), as well as that of the extrinsic variations mainly due to microlensing. The absence of markers at certain lag times indicate that any potential variation was below the noise level. The error bars were estimated by bootstrapping. The SF of the extrinsic variations only catches up with the intrinsic SF at later time lags, which this program of high frequency monitoring takes advantage of by being able to probe lag times below 10 days. The SF is cut at 200 days, the characteristic duration of our monitoring seasons.