Chwałek, Jan
(Wydawnictwo Towarzystwa Naukowego Katolickiego Uniwersytetu Lubelskiego, 1987)
An instrument with 12 keys in an octave can be tuned according to the natural system and as a result 12 consonant triads can be obtained (6 major and 6 m inor ones), each of which consists of natural thirds and fifths. ...