Slope between indices versus correlation for the different pairs of indices (from top to bottom). We show global quantities for all stars (left) and with superposition of the ST slopes for individual seasons (right), for stars for which we have data covering at least six seasons. The ST slopes of a given star all have the same colour. A few stars are indicated with a larger symbol and are discussed in the text: GJ 191 (pink), GJ 87 (purple), and GJ 581 (light blue).