Principle of Correspondence
"This Principle embodies the truth that there is always a Correspondence between the laws and phenomena of the various planes of Being and Life. The old Hermetic axion ran in there words: "As above, so below; as below, so above." And the grasping of this Principle gives one the means of solving many a dark paradox, and hidden secret of Nature. There are planes beyond our knowing, but when we apply the Principle of Correspondence to them we are able to understand much that would otherwise be unknowable to us. This Principle is of universal application and manifestation, on the various planes of the material, mental, and spiritual universe - it is an Universal Law. The ancient Hermetists considered this Principle as one of the most important mental instruments by which man was able to pry aside the obstacles which hid from view the Unknown. Its use even tore aside the Veil of Isis to the extent that a glimpse of the face of the goddess might be caught. Just as a knowledge of the Principles of Geometry enables man to measure distant suns and their movements, while seated in his observatory, so a knowledge of the Principle of Correspondence enables Man to reason intelligently from the Known to the Unknown. Studying the monad, he understands the archangel." (The Kybalion; San Francisco, 1904)
One of the many ways to use this principle is to know that one discrete pitch in one octave is equivalent to another pitch in any other octave - insofar as relative pitch or interval goes. A "C" in one octave is equivalent to "C" in any other octave regardless of specific frequency. In this case the relationship is of the octave or a doubling or halving of frequency. This relativity of relationship holds for any other manifestation of rhythmic energies set in octave relations such as color, music tones, cycles of all kinds and what have you.