Selected spectra in regions around the considered chromospheric lines: an inactive M0.0 star (J14257+236W, black), a moderately active M2.0 star (J18174+483, purple), a very active M3.5 star (J22468+443) in flaring (green) and quiescent state (blue), and a moderately active M7.0 star (J02530+168, orange). The region around the He D₃ and Na D lines (top left panel) in the M7.0 spectrum is not shown because of a low signal-to-noise ratio. Bars mark the line windowranges (solid) and pseudo-continuum ranges (dashed) as given in Table 1. In the case of Hα, we also show the line window and pseudo-continuum ranges used by Jeffers et al. (2018; red) and by Reid et al. (1995) and Alonso-Floriano et al. (2015; blue).