In music, Diatonic, a stepwise arrangement of the seven natural pitches that form an octave without altering a key or mode’s defined pattern. In the case of a diatonic harmonica, they can only play the notes of the two or three scales by default. That means, if you want to be able to play all the scales like a chromatic harmonica, you will need twelve different harmonicas corresponding to different ranges. On the other hand, a chromatic harmonica can technically play all the notes of a chromatic scale. There will be a sliding bar on the side of these models that will allow you to alter the scales.