Simulated correlation (Hα reconstructed from observed Ca II) for all stars versus observed correlation, for hypothesis A (orange) and B (brown) for different definitions: global correlation (upper panel), LT correlation (middle panel), and ST correlation (lower panel). Different symbols correspond to different categories: category #1 (stars), category #2 (diamonds), and category #3 (triangle). The errorbar-like symbols in the y direction represent the range covered when taking the uncertainties on the Hα-Ca II laws into account (see Appendix C.1 to C.3).