Why instruments can be a good thing...

[karbomusic]

And save lots of head scratching. I won't go into detail (yet, though I know some here already know) but I was testing a polarity inversion idea last night and ran into an issue where VRef would get dragged down inconsistently. I grabbed a video repro of it on the scope (video below). IMHO this is one of those issues that would not have shown up most likely until further into the build or even later but the scope called it out and showed the issue in an undeniable manner...

You'll see me flip polarity (top is the control, bottom is circuit under test), and nothing happens, then invert, flip back to in phase and a few seconds later VRef dive bombs taking the waveform with it...