I rem talking to the late, great Bill Keith at a Bluegrass Festival back in the 1980s. He demonstrated those pegs that altered the string's note by a semitone. He was claiming then that they were a Bluegrass "invention". However, lately I read that the Irish Harp had similar pegs. I have seen harpists twist a peg or two when playing and had assumed that they gauged the amount of alteration by repeated use but, perhaps the modern instruments have a type of "Scruggs peg now as well ???