Not long ago, Howard Wainer, a statistician I mentioned recently, learned that his blood sugar was too high. His doctor told him to lose weight or risk losing his sight. He quickly lost about 50 pounds, which put him below 200 pounds. He also started making frequent measurements of his blood sugar, on the order of 6 times per day, with the goal of keeping it low.
It was obvious to him that the conventional (meter-supplied) analysis of these measurements could be improved. The conventional analysis emphasized means. You could get the mean of your last n (20?) readings, for example. That told you how well you were doing, but didn’t help you do better.
Howard, who had written a book about graphical discovery, made a graph: blood sugar versus time. It showed that his measurements could be divided into three parts: