Cathy,
Here is a question I've thought about but not found the answer too.
You have a machine to work on, it's an early one with no reference or timing marks. Say an early Singer 66.
You want to check to make sure the needle is at the correct height, but with no reference or timing marks, what method do you use to do this?
And is there a method that would work say on all mechanical machines including the 15 clones?
Joe