Flux-flux relations for some of the most often used indicators of chromospheric and coronal activity in M stars (Hα, Ca  ii K, X-rays and He  iλ   5876 Å). Same plotting symbols as in Fig. 4. The results of a linear regression fit to all detections and its standard deviation are shown as dash-dotted and dotted lines, respectively. For F_X vs. F_Hα we also show the relation derived in the same way for a sample of field M dwarfs as solid line (see Stelzer et al. 2012a).