Retrieval of the center-of-mass RV vs. orbital phase of the injected signal for the single Fe I line at 539.318 nm. This shows RV results extracted from 2672 line bisectors measured during 10.8 yr. The standard deviation of the points plotted here is 1.7 m s⁻¹, so we do not expect to retrieve the injected signal without averaging over bins in phase, as well as over multiple lines. Because the injected signal has a 1 yr period (with zero RV on January 1), the orbital phase plotted here is the same as the terrestrial yearly calendar. The increase in humidity over Kitt Peak in the summer months affects the RV retrieved from this line, noticeable as increased scatter and a bias toward more positive (redder) RV values during July and August (see text for discussion).