Everything I have read says to get your tension right THEN use the TOWA to find your magic number and adjust the rest of your bobbins to that number.
Are you having problems with your tension? If you are getting loopies on the botton, it's your top thread. On the top loopies it is your bobbin (usually). I try to just play with top thread mostly..... Also some of these machines (mid/long arms that is) have a tendency to loose tension at the end of bobbins, so always start with a full bobbin.
Good luck!