UPDATE 12/29/2011 2:42PM- Deleted old .stl, it was bad, added correct file.These two test pieces are printed with one on the X and one on the Y axis. The idea is that they should both fit each other. Use when your circles come out oval. If the X and Y are not calibrated well this test will show you which is off.Print, insert the X piece into the Y slot and the largest block should fit snugly and vice versa for the Y block and X slot.The blocks are -0.50mm graduated from 25mm long to 23.5mm long. Do not concern yourself with the width of the blocks inside the slots. Only look for the length. (Long ways)Be advised that this test can show you a fitted piece even though the actual steps may be off.For example if both of your axes are off by 3mm the test will show a fitted piece but will measure 22mm at the widest block. It's up to you to put the work in and calibrate for the actual steps per mm.