find below the explanation from the Capriccio manual - the same principle applies with slight variations for all products.
- it shifts your phrase harmonically by the relative interval set in the Harmonic Shift octave if the +/- button for that phrase is set to ON
- it will play the enharmonically correct Minor or Major chord for that step (so the perfect 4th in Major will throw up a Major chord), unless you change that setting in the diagram in options. These settings are global so they apply to all phrases and Harmonic Shift transpositions.
- You can use Harmonic Shift as a 'one finger playback' method by turning Harmonic Shift on for all phrases and only playing your Root chord in the left hand, then using the Harmonic Shift octave for your enharmonic steps within that tonality.