When cutting half-square triangles, 7/8" must be added to the finished size to allow for seam allowance. This ruler helps take the math out of half-square triangles- adding 7/8 inch to the finished size of half-square triangles. Solid black lines are marked at 7/8 inch, 1-7/8 inch, 2-7/8 inch, 3-7/8 inch,4-7/8 inch and 5-7/8 inch for easy cutting of units. Designed by Joyce Dawe. Made in the USA.