That's a pretty handy chart!
I'd make one change on it, though, and that's the inclusion of the 7th chords. Just like the relative minor is listed for each major chord, there is a "relative 7th" for each major chord, too. The minor is denoted by the 6th. The 7th chord is denoted by the 5th.
So for C major, what I would list is the G7. For G major, I'd list D7.
You may also want to consider dropping a copy of this in "Other Stringed Instruments."
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