It's a calibration thing that you print, then you validate the result with the PDF. It tells you if your towers are aligned correctly and your diagonal rods lenght accurate. With these informations, you can then update your delta 3D printer firmware for dimensions accurate printing. . You can use my Marlin4Delta fork for an easy firmware configuration. Repetier is also a good firmware with all necessary parameters. Here is my inspiration and instructions: http://www.thingiverse.com/thing:745523 Also remixed from http://www.thingiverse.com/thing:761799 I'll include these instructions in the PDF later, and if someone can provide proper Repetier instructions, I'll include them in my PDF as well. A big thanks to Taede de Jong (dolpin) for its work and instructions.Remove from bed and place on paper, take care of the aligment. Put measurements on the rectangle boxes and see firmwares or http://www.thingiverse.com/thing:745523/#instructions for more instructions.