Hmm! I wonder about this guy's claim.

I don't know exactly what your chord converter was like, but back in 1952, when I bought my first guitar (a $9.95 Regal with a $5.00 fiberboard case), the guy at Myer's Music threw in a free pick (never used it), a copy of Nick Manoloff's How to Play the Guitar, and a Nick Manoloff, Special Patented Chord Wheel.

It consisted of two round pieces of heavy cardboard about eight inches in diameter, fastened together with an eyelet in the center. The disk on top had rectangular holes in it, labeled "Tonic," Sub-Dominant," "Dominant," plus a couple of other holes with labels like "Dominant 7th," "Double Dominant," etc., and inside that (closer to the center) it had the relative minor chords. The bottom disk had chord diagrams printed on it (major, minor, and 7th chords), arranged in the Circle of Fifths. It was sort of a circular chord slide-rule. Dial a key, and it showed you what chords to play. I absorbed my first knowledge of music theory from that gadget.

I know you can patent gadgets and gizmos, but somehow I don't think anyone can patent or copyright the Circle of Fifths or any other aspect of music theory.

Don Firth