1. An apparatus for use with a process controller, the apparatus comprising: an equation editor adapted to receive equations describing a process to be controlled by the process controller and to generate model information representing the equations; a model factory adapted to receive the model information and generate an equation stack representing the equations; and an equation evaluation engine adapted to receive evaluation information from the process controller, evaluate at least one of the equations using the evaluation information and the equation stack, and send a result of the evaluation to the process controller.