 Grush’s solution drew on concepts from modern control theory. In addition to a controller, a sensor, and a goal state, certain kinds of control systems employ a process model of the actual process being controlled. A process model can facilitate a variety of engineering functions, including overcoming delays in feedback and filtering noise. The accuracy of a process model can be assessed relative to its “plug-compatibility” with the actual process. Plug-compatibility is a measure of the degree to which a controller can causally couple to a process model to produce the same results it would produce by coupling with the actual process. Note that plug-compatibility is not an information relation.