Relation between average indices – without the most active stars – for the three pairs of indices (from top to bottom) and the 3400–3900 K range. The values in ordinates have been shifted vertically to take the temperature effect into account (We selected points with Ca_m around 0.9 (for the two first plots) or Na_m around 0.15 (for the last plot), fitted a linear function to the index versus T_eff and applied the resulting correction to all points.). The red points and lines correspond to averages in bins in abscissa.