Variations in I, Q, and U in J1819+3845 over a succession of years. Each panel shows lightcurves for Stokes I, Q and U. Typical errors are as described in Fig. 7, but about 1.4× smaller due to the increased integration time (60 s as against 30 s). Each epoch was chosen to represent a similar stage in the annual cycle of timescale variations exhibited by the source, facilitating meaningful comparison between epochs. The thin black curves in each of the Q and U panels show a scaled and shifted version of the Stokes I lightcurve for comparison.