Triangulation is the basic tool used with autosomal DNA testing (atDNA) to ascertain if two or more people share a common ancestor. But it can be confusing! Here is a post in The Genetic Genealogist, in which Blaine Bettinger explains just what triangulation is and is not, and shows how to use triangulation successfully to find a common ancestor.

A Triangulation Intervention by Blaine Bettinger