Notes and chords that are a perfect 4th or 5th apart are the foundation of many songs.
Going clockwise around the outer circle of the diagram, notes progressively go up a Perfect 5th.
Going anti-clockwise around the outer circle, notes progressively go up a Perfect 4th.
When each note of the outer circle represents the tonic note of a major scale, the numbers next to them show how many sharps or flats appear in the key signature for that major key.
© Carlos Thrale 2017