Panel a: light curve of MAXI J1820+070 in the V filter (green line with error bars, from AAVSO observations). polarisation measurements are overplotted with pale-coloured symbols. As in Fig. 1, the dates for the polarisation measurements in the B and V filters are shifted by 0.5 d for clarity. The vertical line marks MJD 58222. Panel b: evolution of the Dipol-2 B (blue triangles), V (green diamonds) and R (red crosses) magnitudes, calculated from the relative flux of the target and field star, hence the the zero-point is uncertain.