I have been tricked a few times working on 3 phase with a bad connection. I figured out long ago it is always easier for me to draw a picture of how I think things are wired and transfer the meter readings to the drawing as I do them. For me, seeing it on paper makes more sense that trying to remember what I was looking at and what I got several measurements ago.
If I actually have a wiring diagram and there is a copier nearby I will copy the page I am looking at so I can have one I can write all over.
