Quote Originally Posted by devmonkey View Post
One other thing that occurred to me, how did you ensure you moved the sensor/vice assembly absolutely in a straight line? Any deviation in this procedure would show up as non-linear errors in your linearity measure since it would have been impossible to get the laser perfectly planar with the granite. This applies to both types of laser dot and line. I think you need a precision straight edge as well as the reference surface to check the accuracy of the system.
I used straight edge clamped to the granite, just as you said.

Cheap webcam arrived, useless with lasers, sensor is smaller than the beam, will test it with wire when it gets here.