Mesoamerican calendars prognostic power for the coming year. Therefore, People tried to do as little as possible on these days, and a person who was born during the nemontemi was considered unlucky. Since both the 260-day and the 365-day calendar repeat, approximately every 52 years they reach a common end, and a new Calendar Round begins. This 52-year cycle was the most important for most Mesoamericans, with the apparent exception of the Maya elite until the end of the Classic Era, who gave equal importance to the Mesoamerican Long Count calendar. According to their mythology, at the end of one of these
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