Upper panel: half full amplitude of stellar cycles vs. B–V, derived from Lovis et al. (2011) after revision of the largest amplitudes (see text) for different types of stars: B–V < 0.7 (black stars), 0.7 < B–V < 0.9 (red squares), and B–V > 0.9 (green triangles). The black lines correspond to the lower and upper boundaries that were taken into account in building the grid. Upper panel: same vs. average Log . The solid line represents the lower limit that was taken into account in building the grid.