One of the first things I learned about my Sweet 16 is the bobbin case tension is the foundation tension for the entire machine. It is important that the bottom tension be set correctly before any adjustments are made to the top thread tension. Tension adjustments may need to be made every time different threads are used and even when a bobbin is changed using the same thread. That can be a scary, intimidating, and sometimes frustrating task for many quilters using a mid- or long arm machine for the first time.
There is an easy test for checking bobbin tension and I've included Jamie Wallen's video tutorial below. (I love Jamie's videos and he has some awesome tips and lessons; definitely check out all the uploads on his channel if you have a mid or long arm quilting machine.)
As simple as the drop test is for checking the bobbin tension, it is definitely something that is based on 'feel' and 'judgement'. I'm someone who prefers factual and quantitative answers and I don't have enough confidence just yet to rely on my own assessment of the Sweet 16 tension. Therefore, I bought a TOWA bobbin case tension gauge to get a numerical reading I can use to set the exact tension for each bobbin I use. I ordered it from Superior Threads and while it seems a little pricey, the peace of mind it brings me is worth it. Once you load the bobbin case in the gauge and pull the thread through the pulleys, you get a reading. The tension screw can be adjusted right in the gauge so you can pull and test again until you get the reading you desire. It is very simple to use.
Superior also has a free Longarm Tension Guide PDF that you can print off for reference. I think this will make it so much easier for me to achieve good tension on my machine. The TOWA is made in Japan and comes in L and M bobbin styles. You can watch the video below from Superior to see how it works.