Change in intrinsic Stokes parameters of MAXI J1820+070. The weighted average polarisation is shown before and after MJD 58222 in three filters: B (blue triangles), V (green diamonds), and R (red crosses). The two panels correspond to two different estimates for the ISM polarisation: from the closest field star 2 (see Table 2) (panel a), and from the five-star (2, 3, 6, 7, and 9) average (panel b). Coloured error bars correspond to the error of the mean of the source averages, and grey error bars also include the uncertainties in the estimate of ISM polarisation.