Interfacing. In each model, Microsoft Excel was used to provide a user interface for both input and output. It acts as a common denominator; it’s a simple program that is widely available and well-known by lots of users. As such, it allows the simulations to be used by novices, who can describe scenarios in terms of delivery schedules, component shortages, breakdowns and so on. After a simulation run, the results are exported to that same, familiar application, where the user can examine predefined, graphical readouts, or subject the data to their own analyses.