**2.1. Tasks in design of the GUI screen**

The GUI providing human-computer interaction presents one of the most important parts when working with the system model. User interacts with the computer easily, intuitively, without need for derivation, design, development, composition, and debugging the simulation model; without necessity to learn its operation, and finally, he gets required information in transparent, well-arranged form. In the fact, such GUI presents a functional virtual model, where the user sets system parameters, chooses mode of operation and required outputs to observe results. Design of GUI starts with careful planning of the following tasks:

