For HST you cut 7/8" larger than the finished size, and for QST you cut 1 1/4" larger. So the 3 7/8" square cut diagonally once would result in a 3" piece, and the 4 1/2" square would result in 3.25" finished. They probably want you to cut down the second piece, but then why not also have you make the first one 4" and cut it down?