This set is the 3 missing Solffegio Notes, which work with the original set of 6 forks.
These original sound frequencies were used in Ancient Gregorian Chants. These chants and their special tones were believed to give tremendous spiritual blessings when sung in harmony during religious masses. These frequencies can now be produced with the help of these Sacred Solfeggio Tuning Forks.
174 Hz (=3)
285 Hz (=6)
963 Hz (=9)