OK, so I have made significant progress in my understanding of how to go about this orthogonality thing since starting this thread. I've now started to make something to do the job, working along the lines of Barry's method.
I bought a dial guage today and have made up a stand from metal I had in the shed to form the structure of what will hold the dial guage. See attached pictures. I'll put some bricks on the legs to hold it steady.
Could someone help me out with explanations of how to attach the dial guage to the pole in a way that I can adjust it to the correct height then lock it solid in place?
The guage has 1 inch of travel so I do wonder if I should just bolt it on hard to the pole aiming to have the pin compressed in about 1/2" and not try to have the pin "just touching" the dec axis pins I'm measuring against?
You can see the dial guage has an attachment point at the back.
I've been trying to think of how to have a leaver arm which is attached to a threaded rod or the like. Or just attach the guage directly to a vertical threaded rod some how.
Suggestions appreciated.
Thanks,
Roger.