Summary I printed out a 1 inch calibration cube and got my Printrbot LC calibrated really accurately. Or at least I though so until I printed something with inside features (holes and other openings) which turned out to be way too small. I made this 'cal slab' so I could check a number of sizing parameters after tweaking my printer and Slic3r configurations. It's only 6mm tall because I have had not issues with Z calibration. I also added a number of thin walls to try and get an idea what my actual extrusion width is (which turns out to be much larger than Slic3r thinks) Instructions Print the slab, grab your calipers and compare the actual dimensions to those on the drawing (the pdf file) Designed using Cubify Design. I highly recommend this $200 package for serious designers.