Abstract: A simulation system includes a computer, and provides a mathematical model of the entity under investigation, and includes input apparatus for supplying desired variable change information to the mathematical model. The system generates model simulation information as modified by the variable change information, and controls the changes of the model simulation information in correspondence with real time, independently of the computer used. The system includes toggling apparatus for activating and deactivating selectively desired subsystems of the mathematical model, and is arranged to adjust selectively the number of subsystems and subsystem components of the mathematical model. In addition, the system allows the user to customize the information displayed about the mathematical model while the model is running without deactivating the simulation of any activated subsystem or subsystem component.