It is an excellent tool. However, be sure to verify the absolute calibration of the pivot to spindle dimension. My protractor was off by about 1mm. A setting of 258mm for a VPI arm, was actually 259mm. Easily acounted for by setting the protractor to an indicated value 1mm less than desired.
I verified my protractor by using a metric ruler, and verified the ruler against another ruler.
I verified my protractor by using a metric ruler, and verified the ruler against another ruler.