The machine mix for a particular FMS, the number of machines performing each of three operations and the number of machines performing any of the three operations (flexible machines), is input to an FMS simulation. An intuitively selected combination of these four inputs are compared to a 2**4** minus **1 fractional factorial design. The throughput predicted by the simulation is analyzed through two different regression models. These models are validated. A regression model in two inputs including their interaction, gives valid predictions and stable explanations.
