The author urges the need for a development of a continuous-process technology resting on quantitative rather than qualitative foundations. He suggests definitions of some of the qualitative terms currently employed in the description of process lag and explains that such generally descriptive terms are not indispensable in process analysis. To illustrate the quantitative approach, the author derives integrable equations describing the behavior of some elementary thermal systems, and interprets the solutions as the result of definite operations performed on these systems, particular effort being taken to include detailed steps in the mathematical developments. One type of lag is shown to be expressible, as such, directly in units of time. It is explained that the more general types of lag are best embodied in the structure of a differential equation; while the conventional “time constant” is shown to have meaning only for a restricted class of systems. A method is suggested for the concrete representation of industrial processes by the easily visualized and comparable form of liquid-level systems. By way of exemplification of this method, such liquid-level equivalents are given for the previously considered thermal processes. Gradual development of theorems, guided by quantitative mathematical methods, is held as the only sure road to a practical science.