This keyword defines the axes permutations, ie which axis is the fastest changing, the medium, and the sectioning. The various axes are identified with the following convention : x is 1, y is 2, z is 3. For example, to define a valid permutation for a monoclinic space group with b unique, you give PERM 3 1 2. In this case the first argument of GRID should be the number of divisions of the c axis, followed by the number of divisions along a and, finally, b. NOTE WELL : Changing the axes permutation without careful thinking is a standard way to inverse the chirality of your molecule. GraphEnt will NOT stop you from changing enantiomorph.