When the lines are set up on the seams of the squares the sections of each of 4 squares are cut on a precise angle...then when rejoined in a layout to form pinwheels the entire piecing is all pinwheels all in the same 4 parts of a like square. . . amazing to see happen...and beautifu l to see finished.. . .yet not a tideous process to have so many odd shapes joined and Joyfully so quickly as well...a one day project for sure you'll be so excited to show to others or gift. . .as a table topper or wall hanging if artfully chosen colors of fabric... Some (usually solids),just stand out among the others so neatly... Look at someof the links. For Twister Tool or pinwheels tool . . .