The IUC notation is the notation for the symmetry group adopted by the International Union of Crystallography in 1952. It names the wallpaper groups with a 4 character name. First it has a P or C for primitive or centered groups. Groups are given a number 1, 2, 3, 4, or 6 for the highest order of symmetry. Groups can have one or two reflections, given as vertical mirrors first (horizontal reflection), and horizontal second (vertical reflection). A simple reflection is given an m (mirror), and a glide-reflection is given a g. Place holder 1 are given for an orthogonal direction with no reflections.