I'm not sure if this is the one you mean or if there is a more specific one you are looking for, but
After a 17.5 percent commission to management, Axl and his band mates divvied up the money according to a specific formula, which Axl described once in court. During pre-production for Appetite, Axl said, "Slash devised a system of figuring out who wrote what parts of a song or part of a song. There were four categories, I believe. There was lyrics, melody, music - meaning guitars, bass and rums - and accompaniment and arrangement. And we split each one of those into twenty-five percent. When we had finished, I had forty-one percent, and other people had different amounts."
http://www.heretodaygonetohell.com/articles/showarticle.php?articleid=32