Breakthrough moment in guitar

 

I've been learning and watching this video (Jens Larsen's video on Satin Doll) and working through his shell voicings starting on the 6th and 5th strings.  I realized that there's a consistant relationship between root and 7th and 3rd.  Specifically, I saw that the minor 7th of D (10th fret, 6th string) is the 10th fret of the 4th string... and it's a C (another realization that seems minor... the 7th is the previous note to the root).

The minor third is the 10th fret of the 3rd string.  Ah-ha!  THAT'S what the chord shape of a minor 7th is a straight line on the 10th fret (3rd, 4th, and 6th strings).  

Then I began to make sense of the chord shapes of minor, major, and dominant 7th and what they mean in terms of flats and naturals.  (how they're spelled)

The diagram above is far more complex than what I'm talking about.  And slightly less useful than the actual chord shapes.  But it allows you to see the shapes of intervals.