The general idea of the regression control chart is as follows: Suppose you are monitoring the relationship between the number of parts produced and the number of work hours expended. Within reasonable limits, you may expect that the greater the number of work hours, the more parts are produced. You could randomly draw 5 sample work days from each month, and monitor that relationship. The control limits established in the regression control chart makes it possible for you to detect, when the relationship changes, for example, when productivity drops and more work hours are necessary to produce the same number of parts. See also, Scatterplots.