I'm very lucky and can go by this rule. I have a Viking Diamond Deluxe and it auto adjust so I've never had to worry about that. I know that if I use speciality thread that may change. I've used metallic and it did fine after I took it off the machine and put it in a coffee cup. Bottom line is; if the stitching/thread is messing up on the bottom of fabric it's your top area that has the problem rather its tension or rethreading, etc and if the messing up is on the top, then its the bobbin area which most of the time can be fixed by rethreading the bobbin, rewinding the bobbin or even cleaning it out. I try to make sure my top and bottom thread are of the same type and this helps eliminate problems too. I was told in class this weekend that all spool threads even the small ones should be used standing up. I've never had a problem with them laying down so she said I was lucky. It is another area that I can investigate when I have an issue so its good to know.