Calculate Error from uneven rail and reference

[feldah]

Found a photo of the setup I mentioned, it was just a lashup for a one off, it worked well. Note the bolted on wire support and adjustment unit

I was digging a bit deeper in the wire alignment. It sounds quite interesting as I said. previous. I am considering that in our days even a smartphone camera should do the trick. In my case I can go as close as 7cm without loosing focus. one pixel takes then the picture of a 0,015 mm square. One thing I would be interested in if you could explain the construction for the support of the wire. More in detail. As I see it as difficult to keep it in place.

Further I was reading an article where they recommended to use "stainless steel “down rigger” (fishing line) wire, rated at 150 lb" as this would be better then piano wire.
http://fwrc.msstate.edu/southernsaw/alignment1.pdf

But to pull it that hard with 75% force I would need a very rigid support.