One point for every square a piece can go to plus one point for every supporting piece minus one point for every defending piece.
Thoughts?
So at the start of the game the a-pawns and h-pawns are worth three, the same as knights, while bishops are worth one and rooks are worth zero?
BTW, I am guessing you meant -1 per attacking piece, not per defending piece.
Don’t let me stop you. You use your formula, I’ll use mine.