"The original idea of the autoharp (the "chord-zither"), or so I have been told, was to develop an instrument that [ ] non-musicians [ ] could strum chords for leading group singing."
Actually, as I understand it, it was developed partly for that (after all, it was a selling point, so why not make the claim?), but as well for teaching a new system for writing music. Or at least, Mr. Zimmerman hoped that this new system would catch on. It involved numbers instead of letters, and was intended to make it possible to write without the musical staves (treble clef, bass cleff, etc.). The system was a disaster, and never adopted by more than a handful of hopeful dreamers who couldn't memorize "Every Good Boy Does Fine" and "FACE."
Early autoharps have a number as well as a letter on the chord bars and the chart that sits under the strings. Those numbers were for use in the music-writing/reading scheme that Zimmerman proposed.
Thank God he didn't succeed with the scheme, but luckily, his chord-harp did succeed in its other feature -- an easy-to-use accompaniment instrument. I'm sure countless numbers of people learned a lot about music through use of the autoharp.