I created this part to help with the calibration of the Skeinforge Carve setting for my Cupcake CNC. It is a set of two single-walled, open, stair steps 10 and 20 mm tall and 20x20 mm length and width. By serendipity, the inside wall pulls away from the outside wall as the carve setting gets too high, allowing me to precisely set my Carve to 0.39

WARNING: Your mileage may vary!

Note: the .SDLPRT is in Solidworks 2010 format.