The term “harmonicity” describes the tendency for the length of the next cycle to be related to the former by some orderly factor. Applying this principle varies widely from one analyst to the next, but there are three primary schools of thought.
1) That the cycle periods are related such that their reciprocals are in arithmetical progression (i.e., 1, ½, 1/3, ¼, and so on), thus, the harmonics are the division of the largest cycle into equally spaced cycles. If that makes your head swim, refer to the image below for clarification:
2) That the cycle periods are related by some small number (typically, the number 2 is used). Thus, the harmonics are the division of each successively smaller cycle by two.
3) That the cycle periods are related by numbers in the Fibonacci Sequence (i.e., 1, 2, 3, 5, 8, 13, and so on).
Note: All three systems have the factor “2” for the second cycle, but there are differences as the successive cycles become smaller.