From top to bottom: Observed offset of TH, AR, AR1, and AR2 lines at the two last change of TH-AR HC lamp on HARPS (on 2015-10-07 (left) and on 2018-11-28 (middle)) and the only lamp change on HARPS-N on 2020-06-01 (right). One can clearly see an offset in the position of TH lines between an old and a new lamp, of the order of a few meters-per-second, that goes alongside a much larger effect observed on AR lines. Among those three lamp changes, we observed that the ratio between AR1 and TH lines offset is rather consistant, with values of 21.9, 18.0, and 23.0, which is not the case for AR2 lines and thus the combination of all AR lines (AR1 and AR2).