The Length–Weight Relationship for American Boys and Girls

This is a line graph carrying two sets of data at once, one for boys and one for girls. Length runs along the horizontal axis and median weight up the vertical one. Median means half of all babies weigh more than this and half weigh less.

The two lines sit almost on top of each other, which is itself the finding: at these ages length predicts weight about equally well for both. Point A is the book's reading, a boy of 28 inches weighing about 19 pounds. The slider moves that reading along the axis, and the panel gives both figures at the chosen length. Charts of this shape are what a doctor uses to check whether a child is growing to pattern.