Stokes I (upper left panel), V/I (lower left panel), Q/I (upper right panel), and U/I profile (lower right panel) as a function of wavelength, calculated in the presence of a vertical (θ_B = 0°) magnetic field. The various colored curves represent different field strengths (see legend). The figures in this subsection only show the spectral range centered on the K I D₂ line. For this figure, and the rest of those presented in this work, a two-term atomic model with HFS is considered.