For a given exercise, reference tones are depicted by triangles
on a 8-tone scale, which can be played by pressing
the respective triangle. If an exercise is a major triad, for
example, reference tones are the first third and fifth degree
of the scale (fig.2). Because some beginner users might not
be familiar with musical notation, musical notes are avoided.
In other words, a musical scale is presented only by numbers
in a vertical column. This is a clear and intuitive way for
non-musicians