I've been researching the importance of spin testing arrows/broadheads recently and have made a few discoveries that I want to share.
I started by making the spin testing tool pictured here.

What I found is that I was very hard pressed to find any arrow/broadhead combinations that did not appear to be perfectly straight or darn close to it by using the tool. Then I followed another tip I read about which is to stand the arrows up vertically on a flat surface and give them a good spin. A pretty obvious wobble, undetected by the tool, became apparent with this technique.
Also, surprising to me was that I found all of the arrows I tested to be very straight
but I had 2 (practice) broadheads with wobbles. I know this by process of elimination in testing several broadheads in each arrow. And I also noted that those wobbly broadheads were very inconsistent during my shooting practice but the straight ones hit the target consistently in the same spot.
Having at times had a lot of problems with broadhead shots during practice I definitely learned the importance of spin testing to make sure you are using straight broadheads (in addition to straight arrows) before broadhead tuning your bow.
Any other tips?