Velocities computed with respected to laboratory wavelengths versus line depth. Each point in gray corresponds to a spectral line, averaged over all spectra, after subtraction of a solar gravitational redshift of about 636 m s⁻¹. The error bars indicate the 1-σ dispersion (and not the error on the average). The orange and green stars correspond to the 6768 Ni line (MDI/SOHO) and 6173 Fe line (HMI/SDO) respectively. The red stars show the average velocity in each bin in depth and the yellow line is a third degree polynomial fit on those points following the function proposed by Liebing et al. (2021). The y-scale has been restricted to 2 km s⁻¹, and a few points are off-scale for very small line depths. The orange line is from Liebing et al. (2021) for HARPS spectral resolution and after subtraction of a gravitational redshift of about 636 m s⁻¹, and the brown line is from Reiners et al. (2016), based on high resolution spectra.