The pefect fifth is the C and a G of the Solar Harmonic Set, and it is the first 2 intervals in the Fibronocci Set. That makes this little 2 fork combinination the perfect starting point for those just entering into the world of tuning forks, or a amazing boost to the seasoned practitioner.
Listening to the tones helps to balance the nervous system and also causes shifts on the cellular level by causing "puffing" which is when the cells release nitric oxide which is a key thing for helping the body to relax.
The tones also help open the gate way to the higher self and is a great tool to develope one's intution. It is ideal to use at the begining of mediataion the help achieve the sence of oneness more quickly.
This is the set that can grow with you as you learn more about the forks. You can get an upgrade set that give you the 6 additional tones. The Harmonic Set has a total of 4 forks that overlap with the Fibrionacci set of which there is also an upgrade available.