The tones of this hand tubes consist of the pure overtone series of the Venus tone at 441 Hz.
An overtone series is a series of partials that vibrate simultaneously when a natural tone sounds, thus appearing to us as a single tone.
Such an overtone series is the purest, absolutely harmonic scale. It was not artificially developed by man, as with our well-tempered tuning, but the pitches result directly from the natural laws of vibration. It follows a universal wave principle of the universe and thus makes it perceptible to us in every respect.