I watch chords to find what key to play whistles or smallpipes aong with the guitarist. It usually works well and I find it quite easy, except I went to a session, really a friends birthay party, took my whistles etc ready for whatever came up. I was asked to put a bit of background in behind one performer, no trouble, I'll follow the chords for key. I didn't realise she played a right handed guitar upside down, left handed. I gave up trying to read chords and had to admit defeat and ask. Try it sometime.