Right now I am trying to figure out how my tension should be reassembled on my 31-20. It is funny I was just on your site one minute ago.lol I don't have a lot of problems with tension, but I do know that people will sell their machines because they can't get it right. so many times in ads people will say that the machine works but needs to have tension adjusted. So I know it is a big problem for some people and some machines.
My dealer sends your machine home with stitches stitched out on cotton sandwiched with heavy pellon in the middle so the stitches look great, you get it home and have to change the tension when sewing on normal fabric, not all of us use pellon while quilting or making clothing.lol
I would think it would be neat to have machines to look at with different problems with the tension and then explain what you are seeing and how to fix it.