Top panel: line core shift of Fe I spectral lines, estimated using the recalibrated wavelengths, λ_nist, as reference laboratory wavelengths, measured on HARPS-LFC Moon spectra in the blue chip (blue dots) and in the red chip (red dots), and those measured on 3D hydrodynamical theoretical line profiles (open circles) for the same lines. Line core shifts of the two Fe II lines are displayed as orange symbols. The dotted line shows the zero shift for reference. Bottom panel: line core shift difference of the observed spectral lines and the theoretical line profiles. The black dashed line in both panels shows the theoretical solar GRS. The green dashed-dotted line shows the mean line core shift, v_{GRS, 3D, lc}, of the N = 144 lines at 10 <  EW[mÅ] <  400. The light blue and light yellow regions show the standard deviation, σ_{GRS, 3D, lc}, and the .