Six numbers form a pile. A slider moves a single guess for the whole pile; each number's miss from the guess is drawn as a square whose area is the squared miss, and the score is the average of those areas. A second panel plots the average squared error: a bowl whose lowest point is exactly the pile's average. Readouts split the score into two parts, the pile's own spread, which no guess can change, plus the squared distance from the guess to the average, which is zero only at the average.
Six y’s. Name one number for all of them; every miss gets squared. Slide the guess and watch the bill.