a cross over check
Dont know where I read it anymore, but I found it a good check.
We strive for not entering the arms with much bubbles, but if you do create bubbles its easy to check if you are crossing over.
If you are, you will see the bubbles of the hand entry flowing by in front of your goggles if you look down.
If you enter wider the bubbles are only at the sides, so not near the center.
So obvious, but I never thought about it.