Tuning - Major Diatonic, Part 4

The diatonic harmonica is built with two goals... to have as much of the major scale available and to have as many of the common chords available.

Holes 1-4 the goal is the chord... to have a V Chord for the draw (Holes 1-4 = D G B D) and a I Chord for the blow (Holes 1-4 C E G C), this is why F and A are missing, they are not part of either chord.

Holes 4-10 the scale is the goal and it's complete until the missing B at the high-end. Why is it missing?... to keep the chords aligned.

All blow notes of the harmonica create a I Chord (C Chord). Holes 3-6 draw create a vii-dim7 Chord (B D F A). Holes 4-6 draw create a ii Chord (D F A). if you put all of the draw notes together you get a V9 Chord (G B D F A).

Look this over on the harmonica layout below.

Harmonica
C E G C E G C E G C = BLOW
D G B D F A B D F A = DRAW

Chords
C E G = I Chord
D F A = ii Chord
E G B = iii Chord
F A C = IV Chord
G B D = V Chord (G B D F A = V9 Chord)
A C E = vi Chord
B D F = vii-dim Chord (B D F A = vii-dim 7 Chord)