Thank you for your insights. I have been trying to figure out a good way to determine the accuracy of my PM1440GT mag scales. Fundamentally one has to have an instrument he believes in to compare the other readings to. I have been thinking about doing a comparison to an old laser interferrometer I have,.... if I ever get it to work. I worked in the field of magnetism, as well as data storage for several decades (hard drives, tape etc), but I have not taken one of these scales apart yet to determine exactly what technology they are using and I have not found much of a description of it on line. My guess is that the scale is just a set of a few tracks of magnetic patterns and the transducers are magneto-resistive sensors. If these are really being affected by the magnetic milled waste that is not on the track itself, they must not be shielded from external fields much. Ultimately, the scales can only be as accurate as the magnetic patterns are recorded. So it would be easy not to have great linearity or accuracy over distance.
You did not say how you figured out how to correct for non-linearity. I am curious, but can wait to hear from you when I am back trying to do my own.
Thanks,
Dave
