Question about the 6 1/2 fret
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The MD is a ' Modal ' based instrument, not a ' key ' based one. I think theory has 'diatonic scale' [and its naming conventions] being based on the Ionian Mode and the remaining modes being a reordering of the the Ionian mode. The nut/zero fret sets up the Mixolydian pattern. Fret three sets up the start of the Ionian pattern. Each fret sets up another mode.
This leads me to conclude that, basically:
CDEFGABC is a diatonic scale with its attendant naming conventions, and
DEFGABCD is a modal scale [Dorian] without the naming conventions. I'm wrong probably, but it keeps things simple for me.
Addition of the 6 1/2/13 1/2 permits the Ionian mode to start at the nut/0 fret.