After the steps described above have been completed the routines are ready to accept the input of model data. The first item to be entered is the model header, this is done via a call to the routine DIHED. For new models, DIHED is called indicating that a new model is to be input. For existing models, DIHED may be called indicating that subsequent data sets are to be appended to the model. Nodal Co-ordinates and Element Topology cannot be appended to existing models.