Comparison between observed and theoretical spectra of the M 4.5 dwarf GJ 1224. Upper panel: observed and calculated spectra at the Fe i 8468 Å line (left plot) and the ratio between corresponding magnetic and non-magnetic spectra (right plot). Thick solid line – observations of GJ 1224, violet long-dashed line – observations of inactive LHS 337. Middle and lower panels: same as in Fig. 3. Model parameters: T_eff = 3200 K, log g = 5.0, ε_Fe =  −4.45, υsini = 3 km s^-1. Thick solid line – observations, blue dashed line – B = (2.7,0,0) kG, green dash-dotted – B = (2,0,0) kG, red solid line – B = (1.7,0,0) kG. Wavelengths are in air for upper plots and in vacuum for the middle and lower plots.