It might be that they moved a marker from one pillar to the next each day; in which case, the builders of the structure were trying to figure out some celestial cycle that fit in a 40 to 46 day period. It is probable that the larger ring was used in conjunction with the smaller ring, which in combination would give a cycle lasting 520 days. This is equal to three eclipse half-years and would give the Totonac priests an interval to predict eclipses, with the average interval between extreme rising positions of the moon being about thirteen days. (Malmstrom, "A New Interpretation of the Stone Rings...

They were able to accomplish this by moving some kind of marker along each stepped pillar of the largest and smallest ring each day.
WORKS CITED

Foster, Lynn V. A Brief History of Mexico: Updated Edition. New York: Checkmark Books, 2007.

Malmstrom, Vincent H. A New Interpretation of the Stone Rings of Zempoala. n.d. 5 Dec. 2011.