Stokes V/I profiles as a function of wavelength, for the spectral ranges centered on the K I D₂ (left panels) and D₁ (right panels) lines, respectively. Upper panels: an LOS of μ = 1 is considered in the presence of vertical magnetic fields. Lower panels: an LOS of μ = 0.2 is considered in the presence of horizontal fields with azimuth χ_B = 0°. A field strength of 200 G is considered for both geometries. The results of RT calculations accounting for HFS and accounting for the Paschen-Back (PB) effect (black solid curves) are compared to calculations neglecting HFS in the atomic model (red dashed-dotted curves) and calculations accounting for HFS but making the linear Zeeman splitting (LZS) approximation as described in the text (blue solid curves).