Relative changes of Fe I and Fe II absorption line equivalent widths during the measured periods in 2016 (red), 2017 (cyan), and 2018 (gray). Left column shows the dependence on the Mt.Wilson Ca II H & K chromospheric activity S-index; right column on the radial velocity as obtained from the full HARPS-N spectrum. A lower S/N in the grating orders housing weaker lines at the longest wavelengths accounts for a greater spread of points in the bottom frames. The lines included in each group are listed in Table B.1.