Review on Findmall Professional Precision Machinists Toolmakers by Bill Forbis

I bought this to align my CNC router (pcnc440) and my Craftsman 12"X24" lathe. There were no issues with the level accuracy, no calibration was required. As others have suggested you can test it on a more or less flat surface by reading it and then rotating it 180 degrees and comparing the two readings. Mine was dead. The level is sensitive enough to pick up the smallest rotation of the leveling feet on any machine I can make, somewhere around 1-2 degrees of rotation. Definitely recommend.