The magnitude scale of an girl's ass. The best ass can be a Milton Bradley, and you subtract a letter from the name as the ass gets worse and worse. A mediocre ass would be a "Milt", because you have subtracted the "on Bradley" from Milton Bradley. An abbreviation can just be Milton for a good ass.
Jim: "Yo she got a Milton Bradley."
Bobby: "Nah, man, that's only a Milto, it doesn't the girth."