US Patent 8378195 Chord teaching apparatus

The invention provides a musical indicating device for finding the 12 most common chord types and their inversions on string and fretted musical instruments. It can be generally formed as a thin sheet-like base member with a front featuring 12 different transparent chord dials that are each pivotally attached to the base member over a color-coded, pie-shaped diagram of the Willoughby Scale/Chromatic Scale. On the back is a transparent Diatonic Octave Dial pivotally attached to the base member over a color-coded diagram of the Chromatic Scale/Willoughby Scale with the Key Signatures surrounding the diagram. The octave dial has selectively aligned indicia that represent the notes of the major form of the diatonic scale.