Major thirds tuning

The M3 is tuned in fourth fret all the way up so from low to high the open strings become E-Ab-C-E-Ab-C-E. Since the top and bottom strings are E's two octaves apart, the range of notes at your disposal is the same as on a 6-string guitar in conventional tuning. However, gone is the exceptional interval between the 2nd and 3rd string (four semitones as opposed to five semitones between all other pairs of strings) that breaks the symmetry.