Long-term evolution of the magnetic flux density measured from Zeeman broadening modelling. The data point format is the same as Fig. 2, and for each epoch we overplotted the mean value and standard deviation as error bar. There is an overall trend that reflects the variations of B₁ across both optical and near-infrared data. In addition, for the near-infrared SPIRou time series, we also observe the same oscillating behaviour found for the FWHM of Stokes I.