Octave-of-Following (OOF) state is the state in which a fretted note is the octave of the following open string.
This is true:
E-string-1 at Fret-7 is a B-note with OOF state re B-string-2
*B-string-2 at Fret-8 is a G-note with OOF state re G-string-3
G-string-3 at Fret-7 is a D-note with OOF state re D-string-4
D-string-4 at Fret-7 is an A-note with OOF state re A-string-5
A-string-5 at Fret-7 is an E-note with OOF state re E-string-6
*OOF state occurs at Fret-7 often enough to be useful for raising note consciousness. The exception is on B-string-2. The interval between G-string-3 and B-string-2 is the only interval that isn’t a Perfect-Fourth; it’s a Major-Third. Therefore, OOF state is a half-step higher at Fret-8.
And there you have it. It’s time now for Derived Octave-of-Following (DOOF) state — coming next.
(c) 2019 JMN