Guitar Theory - Blue Note and Blues Scale - 6 half steps

In this exercise, we practice chord and finger shapes centered on using the Blue note, which is 6 half steps above the root note, and also 6 half steps below the octave note...

Not only is the Blue note exactly half way in between the root note and the octave note,

The Blue note is also exactly half way in between the Perfect 4th and Perfect 5th.