Left panel: variation of the active region velocity with the magnetic field strength B for different stellar types and measurement methods. Right panel: MHD line profile of the FeI line at 6165 Å for different magnetic field strength (solid lines) and line center measurements with the Gaussian method (crosses) and the centroid method (x). The color code for the line profiles and the center measurements are the same: black for B = 0 G, green for B = 20 G, blue for B =100 G, and red for B = 500 G.