Magnetic diffraction Systematic Absences for the group Cmc'21' (#36.175) For this space group, BNS and OG settings coincide. Its label in the OG setting is given as: Cmc'21' (#36.4.252)
Values of h, k, l:  h integer, k integer, l integer
Systematic absences for general reflections (produced by centrings):
Diffraction vector type: (h k l) -> Systematic absence: h + k = 2n + 1