Left: Evolution of the Stokes parameters, polarization degree and angle. Top right: q − u plane. Weighted mean of the source observations (black circles), calculated yearly, and of the field stars (red cross). Bottom right: Empirical distribution function (EDF) of measured polarization using all data points (black line) or the weighted averaged points (red line) compared with expected cumulative distribution function (CDF) of polarization measurements (blue line). The data shown correspond to the BeXB RX J0146.9+6121.