tension is good and consistent around the chain ring.

It just makes sense that the chain line is off. Looking down from above the chain, the chain is catching the top of my chain ring with the chain being towards the bike... there is a small gap of course, and the chain is getting pulled away from the frame, so to speak.
When the bottom of the cog grabs the chain, it is pulling it back towards the bike. I'd say there is a barely noticeable crooked chain line

I read a lot about 42.5mm chain lines, etc. How is that measured?

Is there a good measuring tool that is inexpensive? Thanks!