On any open string the "octave up" harmonic is on the 12th fret because it's exactly halfway between the bridge and the nut. If you then you fret the 3rd fret with your left hand, the "octave up" harmonic will be on the 15th fret, and so on. That means that if you barre across the 3rd fret with your left hand's 1st finger, you can play the one-handed minor scale in the key of G minor. If you barre across the 5th fret you'll be playing the right hand harmonics in the 17th fret, and it will be an A minor scale.