rings of the inner rotatable disk 17 that is 41 and 42 respectively have sectors indicating the notes of a major or minor scale designated with 34 m 34 and 34 m 34 naturally each of the scales has seven notes for example with the root sector 29a located or juxtaposed with the 34 c 34 of the outer ring 28 the other notes of the 34 c major 34 scale are d e f g a and b again still referring to the situation where the rotatable disk is in the c scale position that is with the root sector 29 39 a in that position opposite the key note c a major triad is indicated by following around in the 34 major 34 ring to the marked sectors these show the other notes of the 34 c major 34 chord which are respectively e and g with respect to a c minor chord the other notes are e flat and g with respect to the dominant seventh chord in the key of c in addition to the root note of c the other notes following around in that specific ring and looking at the marked indicia the notes are e g and b flat similarly the diminished and augmented chords are appropriately marked rotation of the disk 17 to any other scale for example a d scale will allow.