Real life systems don't have to be physical. You can do a lot by playing around with digital PID controllers, graphing the sensor value over time and seeing how

Real life systems don't have to be physical. You can do a lot by playing around with digital PID controllers, graphing the sensor value over time and seeing how the graph changes as a response to changes in the gains. The benefit of this approach is that anyone with some programming skills can do it right away without any hardware.