International
Tables for Crystallography Volume E Subperiodic groups Edited by V. Kopský and D. B. Litvin © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. E, ch. 1.2, pp. 78
Section 1.2.4. International (Hermann–Mauguin) symbols for subperiodic groups^{a}Department of Physics, University of the South Pacific, Suva, Fiji, and Institute of Physics, The Academy of Sciences of the Czech Republic, Na Slovance 2, PO Box 24, 180 40 Prague 8, Czech Republic, and ^{b}Department of Physics, Penn State Berks Campus, The Pennsylvania State University, PO Box 7009, Reading, PA 196106009, USA 
Both the short and the full Hermann–Mauguin symbols consist of two parts: (i) a letter indicating the centring type of the conventional cell, and (ii) a set of characters indicating symmetry elements of the subperiodic group.

Each position in the Hermann–Mauguin symbol contains one or two characters designating symmetry elements, axes and planes that occur for the corresponding crystallographic symmetry direction. Symmetry planes are represented by their normals; if a symmetry axis and a normal to a symmetry plane are parallel, the two characters are separated by a slash, e.g. the 4/m in (R40). Crystallographic symmetry directions that carry no symmetry elements are denoted by the symbol `1', e.g. p3m1 (L69) and p112 (L2). If no misinterpretation is possible, entries `1' at the end of the symbol are omitted, as in p4 (L49) instead of p411. Subperiodic groups that have in addition to translations no symmetry directions or only centres of symmetry have only one entry after the centring letter. These are the layergroup types p1 (L1) and (L2), the rodgroup types (R1) and (R2), and the frieze group (F1).