G Whole Half Diminished — Puerto Rican Cuatro (Antiguo A-D-G-C-F)

G Whole Half Diminished is 8 notes to the octave (symmetric family), drawn here across the Puerto Rican Cuatro (Antiguo A-D-G-C-F)'s A-D-G-C-F strings with every G marked, so home stays visible from anywhere in the pattern.

Unstable and eerie — alternating whole and half steps, with the b3, b5, and 6 spelling a diminished seventh chord in every direction. Ominous, symmetrical, and unresolved.

Heard in: Diminished seventh chords in classical and jazz, horror and suspense scores, Bartok and Stravinsky, and neoclassical metal.

Five courses spanning a minor thirteenth give a scale room to breathe: three or four notes to a course in first position, and a top string clear enough that a melody can live there while the rest of the grip stays down. These maps light every root so a run knows where home is before it leaves.

Work it in one position before you work it up the neck. The doubled courses forgive nothing: a fret held half a millimetre short buzzes on one string of the pair and rings on the other, and that difference is audible long before the run is fast.