The method used to forecast the periods is consistent and accurate in it's results because the construction of the Zodiac incorporates within it's "geometry of time" the periods that structure the human experience of time; the day, the month, and the year with it's seasons. The day, month, and yearly rhythms have also been shown in many studies to affect biological and psychological events in human as well as other species.
The additional element was to use 7 years as the total length of one LifeCycle, which in turn necessitated a nested structure of twelve 7 month Zodiac Phases, and 7 days between Challenge Days.
The initial reason for this was being aware of the sacred nature ascribed to the number 7 by many ancient cultures around the world. See HERE; as well as the historical recognition of 7 years related to the rather ancient idea of "the ages of man" as immortalized in a Shakespeare play HERE and further down on the same page by the ancient greek philosopher Solon as quoted in the section "On the Ages of Man". Seven year stages of life was a generally accepted notion historically and became incorporated into Rudolph Steiner's theory of human development occurring in 7 year stages as outlined HERE.
There is a strong rationale for assuming that the evolution of any process requires 7 stages or periods based on valid science and not just historical tradition. See the section HERE for additional information as to why the use of "seven-ness" is not at all arbitrary.
The links below will provide the additional sources that I have researched that, from my perspective, justifies the use of 7 periods of time or 7 stages as representing the requirement for the evolution of any whole process. The links will pull up popup windows at the midpoint of the window. Click the link again to close the popup.
My name is Robert Lohmeyer. My interest in this area of forecasting spans 40 years. The application is a very useful tool in and of itself and I am happy to offer it. Feel free to reach out with comments, suggestions, and general questions. I always attempt to follow up.