Left: number of thorium lines used over time to perform the wavelength solution in the old and new HARPS-N DRS. Here, we show the results for all thorium–thorium and thorium–Fabry-Pérot calibrations. We see that there is a significant variation in the number of lines used in the old HARPS-N DRS, 16%, while in the new HARPS-N DRS, we nearly always used 2041 thorium lines. Right: RV difference between the wavelength solutions obtained with the old HARPS-N DRS and the new one, which uses the drift map method with the new set of thorium lines.