Q. What is the Professional mode?
A. The Professional mode is identical to the Standard mode, with one exception. Besides the seven piano white keys of the Standard mode, the Professional mode includes the five piano black keys, as well, thereby enabling the user to play any chord that can be played on a piano, as long as the bass note of that chord resides in the currently selected musical key.
Q. How do I toggle the Professional mode ON and OFF?
A. Make sure that the Song mode is OFF (either Song button will NOT be shown or Song button color will be White) and that the Chord mode is OFF (Chord button color will be White). Then double-tap the Pro button to toggle the Professional mode ON (Pro button color changes from White to Blue) and OFF (Pro button color changes from Blue to White).