This is cool. Twist the outside dial to transpose the tonal centre of your key. Twist the inner dial to shift the mode of the scale. Turn on- or off- individual tones to shift into more-exotic modes. Use triangles to illustrate the triads of your major, minor, and sustained chords, or add the sixth or seventh with the help of a trapezoid.
The amateur music theorist in me continually struggles to visualise what and why a key is what it is. This kind of thing helps. Plus, what a cool software toy!