one of the things that really helped me when I got the towa gauge, I discovered that the five original bobbins that came with my machine did not spin freely. When put in the gauge, it would go between 200-300 as I pulled. All my later purchased bobbins (purchased from HQ also) were fine. I really liked those early bobbins as they were a bit heavier duty, so I used them all the time - no wonder tension was such a mystery for me!
Now I have them with my serger, to use as mini spools as needed.