Dave, your two books are the best books about chord progressions I’ve encountered. Thank you. But I have to say your inversion notation is non-intuitive to me.
I understand it is “correct” and “common”, and I get the maths behind it, but it doesn’t help me as a guitar-based songwriter at all. It’s the only feature of Hookpad that I don’t like.
And I love Hookpad. The highlighted chord scale degrees (“Stable” feature) are wonderful.
FWIW, my personal notation for a C-over-G chord (2nd inversion) in the key of G would be C/5(1) - meaning the bass note is the 5 of the C chord and the 1 of the key. The abstracted form would be V/5(1).
#justsayin