Caliper add-on for Westcott Stainless Steel Ruler

This is a remix of [This thing](http://www.thingiverse.com/thing:161702). His caliper system didn't work on the widely used Westcott Stainless Steel Rulers with that non-slip cork base I see everywhere ([Like here](http://www.staples.com/office/supplies/StaplesProductDisplay?partNumber=103960)). I modified it to fit that ruler.