Left (panel a)): PC1 versus PC2 diagram. The colour indicates the SpT. The symbols used are the same as in Fig. 4. The cross indicates the median uncertainties, which have been calculated by propagating the uncertainties through the lineal combination of the input data (EWs and bandheads) with the coefficients calculated. Right (panel b)): the same as left figure, but here the colour indicates the luminosity class.