Moving left to right, harpejji strings increase in whole tones (C,D,E,F#,G#,A#,C,etc.). The frets increase in semitones (C, C#, D, D#, etc.) as you move away from the player. Having both whole tones and semitones nearby is very handy! Click on the picture above to view the Harpejji Practice Poster.
The white markers on the harpejji represent the naturals, or the white notes on a piano. C notes are indicated by hollow white markers. The black markers represent the accidentals, or the black notes on a piano. Clusters of two black notes are C# and D#, while clusters of three black notes are F#, G#, A#, as on a piano.