Magnetic diffraction Systematic Absences for the group Cm'c21' (#36.174) For this space group, BNS and OG settings coincide. Its label in the OG setting is given as: Cm'c21' (#36.3.251)
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