Much of what has gone before in this book is not specific to batch control. Any control engineer could have used this material as a warm-up for any discussion of process control. That is because we have not discussed recipes. Continuous processes have them, but a continuous process is just a static batch process, forever locked in the same place in the procedure, like Bill Murray in Groundhog Day.

The Latin root for recipe means take, which doesn't make much sense unless it is read as a procedure. Take one measure of saltpeter, one quarter measure of charcoal, and one quarter measure of sulfur, add some water to form a slurry, and mix well, then dry. This, loosely, is the "formula" found by Chinese alchemists for gunpowder (ca. 1000 AD), and then by the English alchemist Roger Bacon circa 1250. Sadly, civilization was not ready for the Bacon Prize for Peace. In another meaning of take, a medical prescription is abbreviated as R with a cross through the tail of the R. The crossed line stood for Jupiter, and the pair meant a recipe for making you well, Jupiter willing, if you take it as prescribed.