The Sigma Curve
In the final novel of the Blessing series, Turly Blessing makes his way through arid valleys and up and over the dreaded Lower Mountains, where he meets and endures things through which no man should have to go. But the Blessing papers, and the traditions of his father, mold Turly in subtle ways he finds hard to understand. But as he approaches the old Blessing burial ground where many secrets are contained, Turly understands at last that he must face the final test for the future of all things in the rise and fall of the Sigma curve.
A Sigma curve is a curve shaped more or less like this: S. Read the book and find out what that means.