Stokes I (upper left panel), V/I (lower left panel), Q/I (upper right panel), and U/I (lower right panel) profiles as a function of wavelength. The various solid colored curves represent the results of RT calculations (see main text) in the presence of horizontal (θ_B = 90°) magnetic fields with χ_B = 0° and strengths up to 750 G (see legend). The considered spectral range is centered on the K I D₂ line. The colored dotted curves in the lower left panel represent the V/I profile obtained through the magnetograph formula, for the field strengths shown in the legend.