Application of the SDM using the hmi.ME_720s_fd10 series and Eq. (5). Panel a: sign function ζ saturated at ±5. Panel b: corresponding SDM-disambiguated vector magnetogram, with B_los saturated at ±1500 G in grayscale and red and blue arrows representing the transverse field at positive and negative B_los (same as Fig. 4a). The rectangles in panel b indicate the areas of suspicious disambiguations discussed in Sect. 4.2 (black) and Sect. 4.2.1 (orange and green). In both panels, the 400 G isoline of the SO/PHI-HRT |B_los| is drawn as a solid yellow line.