Radial velocity RMS as a function of the stellar surface gravity. Individual small dots represent the values for the 129 055 stars of the APOGEE sample studied in Tayar et al. (2019). For this stellar sample, the RV RMS was computed based on Eq. (7) (Cegla et al. 2014). The two big dots represent the RV RMS predicted from Eq. (7) for HD 67458 and HD 88595. The star symbol represents the RV RMS predicted from Eq. (7) for the Sun. The color code for all targets represents the stellar metallicity [Fe/H]. The blue and red horizontal dashed lines show the RV RMS values inferred from ESPRESSO observations of HD 88595 and HD 67458, respectively.