The tracker is a fundamental structure. When you pour milk into a glass, you are managing the level so that it tracks your target level.
When you drive your car, you manage your position as to track the bends in the road. You also manage the velocity of the car so that it tracks the speed limit. Your thermostat (or air conditioner) helps the temperature in your car track your target temperature.
Trackers have several structural elements, including:
Trackers have several parameters, including:
In the applet above, you can change these parameters to get some hands-on experience with the tracker. You can likely find a set of parameters that produces a graph similar to the one you obtain with the milk model.
Note: You can set the flow to one-way as in the milk model; milk does not flow back up into the carton from the glass. Two-way flow might represent your position on a road, as you gently swing back-and-forth on either side of your target position in the middle of the lane.
As you experiment, you might notice the limitations that the delay in responding to feedback (the lag) places on how vigorously you respond to the feedback (the gain = the inverse of the time constant). The combination of high gain and large lag can produce overshoot and cyclic behavior.
You can also begin to notice all the trackers that populate your own experience. Trackers control your position, your velocity, your weight, your net worth, and anything that involves moving something from one state to another.
Mathematically, management is the art and science of building and implementing trackers. Overshoot and cyclical behavior typically results from policies that feature high gain and long lag.
Steamship Captains that have to get their boats to the dock, and no further than the dock, know the importance of keeping response proportional to delay. To the extent that those who manage our economy respond with disproportionate vigor, they may risk entraining instability.
Perhaps you can find a combination of parameters that produces rapid rise, overshoot and then continuing oscillation with damping until it reaches equilibrium. This is similar in structure and behavior to the "wedge" pattern in technical charting.