It is a combination of tuning that requires intervals of 3 or inverted by 6, that give easy major-minor triads and at the same time the tuning by 5's (or Bouzouki 5-4).
For a 4-courses instrument like Bouzouki etc it can be with a slight inversion in the lower triad chords E.g.
(E2:E2)-(C3:C3)-(G3:G3)-(D4:D4) (6M-5-5)
OR
(F2:F2)-(D3:D3)-(A3:A3)-(E4:E4) (6M-5-5)
(if used to tambouras or mandolin)
Or if we are used to Bouzouki (which is also open D minor)
(F2:F2)-(D3:D3)-(A3:A3)-(D4:D4) (6M-5-4)
The only reasons that one would prefer the later from the former is that the (A3:A3)-(D4:D4) allows for easy two notes chords by intervals of 3. Nevertheless, it loses its uniformity for solos in the higher 3 strings, and also some major-minor triads on them playable at 2 or 3 frets. Personally, I would prefer the
(F2:F2)-(D3:D3)-(A3:A3)-(E4:E4) (6M-5-5)
The only reasons that one would prefer the later from the former is that the (A3:A3)-(D4:D4) allows for easy two notes chords by intervals of 3. Nevertheless, it loses its uniformity for solos in the higher 3 strings, and also some major-minor triads on them playable at 2 or 3 frets. Personally, I would prefer the
(F2:F2)-(D3:D3)-(A3:A3)-(E4:E4) (6M-5-5)
The 5 main advantages for HARMONIC AND MELODIC IMPROVISATION of this tuning are:
1) It allows for the ancient isocratic accompanying of fast melodies with an interval of 5 by the two immediate lower strings of the string of the melody in the -5-5 part
2) The 2-octaves 7-notes scale by alternating intervals of 3 that shape the triad chords in a diatonic scale (called also melodic corridor or wheel by 3rds see post 94 and 79 ) have symmetric representations in this tuning in the -5-5 part .
3) It is uniform tuning for melodies to shift among the strings in the -5-5 part .
4) The shift higher or lower by an interval of 4 or 5 vertical to strings which is usually a mutation of a melodic theme played horizontally on a string is very easy and symmetric in the higher 3 strings
5) It allows for both melodic improvisation with isocratic accompanying by intervals of 5 and harmonic improvisation with easy to play in 1 or 2 frets major-minor triads in the lower 3 strings.
6) It allows strumming only
