Zeeman RV signature of co-rotating magnetic spots calculated from polarized radiative transfer over several wavelength bands. Stars and filled circles indicate the six wavelength bands where the RV signature was measured, a fit to the first five bands using a straight line is shown as a solid line for each case (the CO band is not included in the fit). Dashed lines show the scaling expected from our our toy model, i.e., a = 2 in Eq. (3).