Discrete-event simulation has been proposed as a tool for the real-time selection of dispatching rules in the scheduling of flexible manufacturing systems (FMS). In this approach, a look-ahead simulation is used to predict the trajectory of the system under different dispatching rules. Then a rule is selected for use in the FMS, based on the performance criterion associated with each trajectory. However, this raises the issue of the criterion to be used for the selection of the rules. A simulation model of an FMS was used to test the effect of rule selection procedure on two performance measures. This simulator was run using four scheduling policies and the performance of the FMS was measured. The main finding of this research is that the use of global criteria gives better results than the use of local criteria.