The Square in a Square® Technique Ruler greatly facilitates the Square in a Square® technique. This ruler is 9" x 12" of heavy plastic entirely suitable for rotary cutting. It includes the three angles 60, 90 and 120 degrees the necessary to achieve the 20 options currently available. It comes with an instruction folder, which includes the first seven Options. Everything we do is based on this ruler!! It does all the triangle units and in multiple sizes. This is the first product you should purchase.