DebraK is correct....the TOWA top gauge isn't worth the money.
Jamie Wallen has an excellent YouTube video explaining how to deal with tension on a long arm. I use all kinds of threads and by using his method, my tension is darn near perfect (and if it is off, that usually means there is lint lurking in the bobbin case).
http://www.youtube.com/watch?v=Q1mRhcquZTM