The 'best' unit cell for monoclinic structures consistent with b axis unique and cell choice 1 ofInternational Tables for Crystallography (1983)

Diagrams with the c/a ratio as ordinate and cos (180° - β) as abscissa are given, which allow one to find out how a given monoclinic unit cell can be transformed so that a and c are the shortest translation vectors compatible with the symmetry of the space group in a setting corresponding to the standard space-group symbol given in International Tables for Crystallography [Vol. A. (1983). Dordrecht: Reidel] [denoted as IT(1983)], which means b axis unique and cell choice 1 where applicable. The diagrams contain the transformation matrices and indicate whether the origin of the transformed cell has to be shifted in order to obtain a structure description with the Wyckoff positions listed in IT (1983). A 'best' monoclinic unit cell consistent with cell choice 1 is one of the requirements for a standardized description of crystal-structure data according to Parthé & Gelato [Acta Cryst. (1984), A40, 169-183].