The Mayan/Meso-American calendar ranges from the Venus cycle all the way to the cycle of precession and beyond. Mayan math is a 20 base system. The calendar is based on the Baktun. Each Baktun has an astrological attachment. It's an amazing system. The system consists of several parallel calendars, and a year divided into 13 months of 28 days.

If you ever get the chance, get to Guatemala. It's affordable and fascinating. Speaking Spanish and some of the local dialect really helps. I was (am) studying K'ich'e; the highland dialect. Difficult language.

For a geologist, the formations and volcanoes of Guatemala are incredible.

It's incredible to think that the Mayan libraries were destroyed during the Spanish take-over of the lands. There are some surviving manuscripts. However, the knowledge that was lost is staggering.