The program NCS handles the constraint or restraint of noncrystallographic symmetry. It is well encapsulated by the shell scripts supplied with the TNT distribution ($tntbin/tnt_cycle_ncs, ncs, gather, and scatter). To constrain a model to noncrystallographic symmetry you need to modify a refinement script to meet your needs. A prototypical script is supplied in tnt/doc/tnt_cycle_con_ncs and the required changes are described in the ``Defining Noncrystallographic Symmetry" chapter of the TNT Users' Guide.