Finally, in order to highlight potential errors in the current model of the structure, each module can list those atoms that most seriously violate the restraints of the refinement. The stereochemistry module lists, for each class of geometrical restraint, the worst discrepancies between the model and the `ideal' values. Similarly, the crystallographic module can list those atoms with the largest positional, temperature-factor or occupancy gradient. Experience has shown that these lists are particularly helpful in pointing out areas of the model that are likely to be in error and may need to be corrected manually.