DES requires the modeler to form questions in terms of the "things that happen" rather than formulating equations. But what exactly are the terms used to describe the things that happen? Recall the description of DES in section 1.0.1, as a "method of empirically determining probabilities by means of experimentation." In general, every action and the response to these actions vary between instances and individuals. A good simulation will therefore incorporate varience into the transition functions and event generation. And of course, the varience has to be based on observed phenomena.
So far, this tutorial has represented DES as a visual presentation of the simulated action. Though we can use DES this way, the EST implementations use DES as a means of finding statistically significant trends based on stochastic processes. The following demonstration will allow you to incorporate varience into the movement model we have been using, and it will show a more realistic view of a simulation's output.