Hi Marion, obviously, I've been far from enlightnening anyone, which is sad. Those differently ascending and descending lines Arto and me mentioned have nothing whatsoever to do with temperaments and/or Pythagorean comma (like low major thirds differing from high diminished fourths or so). And you are certainly right in saying that tones on fretted instruments are fixed.
-- Cheers, Mathias -- To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
