15"x15" Omnigrid rulers are made of durable acrylic plastic with both yellow and black printing which allows the user to see the grid on both light and dark fabrics. There is a left- and right-handed numbering system and the bias lines are oriented to the bottom of the ruler. This eliminates flipping and turning the ruler to use both sets of the diagonal lines. Omnigrid rulers are extremely accurate. Each ruler is laser cut to within .002 inch accuracy. Cut oversized squares and check the finished size of sewn quilt blocks as well as oversized rectangles large triangles.