there has always been an "entry " level, where sometimes a .5 will sell same as a 1.5, depending on whats available etc...and higher grade has always behaved with more exponential quality...but when I started this in 2001 at sdcc, it was more for me to know , "ok, I can sell a hulk 1, in 4.0 for 4K...so as long as I see a copy that is less than 1K a grade point, I can buy to resell"....then I created little notes for me...it worked great on most all books to about 6.0 and then I did a 1.5x factor etc...thats how the entire "price per point" terminology came about...