Hah! I love that there's another PSG player on HN who gets this right away... that's awesome. I never heard of this system specifically... I feel like a singer holding up 3, 4 or 5 fingers has been the way I've been cued lots of times to changes in a song I barely knew, without me even thinking that was a system. I bet they didn't either. Separately, I know zero music theory... but PSG really was what let my brain get comfortable with a 3rd of a 4th being a 6th that was two frets down from the 5th of the root... I think probably engaging your knees and ankles in reaching for the physical positions in time builds almost like a muscle memory of the musical relationships... like the kind of control you get driving a manual car... but only if you already have the tones you're looking for in your head, and you know where you're going. PSG is the most mindbending realtime puzzle to play... so it makes sense that players need tricks to know where to go from a certain position (especially if you find yourself stuck in one when you jump into a song)

I learned about that in the Paul Franklin online course (expensive, but worth the money if you are unable to find a personnal teacher, yay europe). I don't have absolute pitch (and a crappy relative one), but this "standardisation" based on the root note really helps build a knowledge of how chord changes "feel". I suspect this is what builds this ability to easily find the right notes when improvising. Weel anyway, always happy to find people keeping the steel alive !