As you have already seen, adding a call to SU_ADD for a support system is all that is required to activate it ready to be used. For example, if you want the geometry routines for the main detector you should add the SU GEO. This will require loading of all titles files containing the GEDS and GEDP banks. Then within the main USER and its dependent routines you can use calls to routines such as GE_NEXT.