Mesoamerican Long Count calendar number (portion of the DN preceding era date) 7.2.14.19<br> Add Ring number to the ring number date to reach 13.0.0.0.0 Thompson contains a table of typical long reckonings after Satterwaite. The "Serpent Numbers" in the Dresden codex pp. 61–69 is a table of dates using a base date of 1.18.1.8.0.16 in the prior era (5,482,096 days). Mesoamerican Long Count calendar The Mesoamerican Long Count calendar is a non-repeating, vigesimal (base-20) and base-18 calendar used by several pre-Columbian Mesoamerican cultures, most notably the Maya. For this reason, it is often known as the Maya (or Mayan) Long Count calendar. Using a
Mesoamerican calendars menstrual period and birth, unlike Naegele's rule which is 40 weeks (280 days) between the "last" menstrual period and birth. It is postulated that midwives originally developed the calendar to predict babies' expected birth dates. A third theory comes from understanding of astronomy, geography and paleontology. The mesoamerican calendar probably originated with the Olmecs, and a settlement existed at Izapa, in southeast Chiapas Mexico, before 1200 BCE. There, at a latitude of about 15° N, the Sun passes through zenith twice a year, and there are 260 days between zenithal passages, and gnomons (used generally for observing the path of