For those of you who don't have any musical knowledge, the perfect fifth is the best sounding sound interval to the common ear. It is the key ingredient in structuring chords based around the root. With a 3:2 ratio, it creates a nice and pleasing sound to the ear. The most common example of a perfect fifth is a C to a G. Kepler himself, founder of the planetary laws, researched the beat frequencies of the error bound for an imperfect fifth tuning. Just a slight slip-up in tuning can create an unpleasing sound for the human ear. Posted below is a link to the wikepedia page where you can learn more about this interval and also listen to it.