Question: How long and in what capacity did Joachim Rittstieg study a system of calenders used in pre-Columbian Mesoamerica?
Sentence (from "Maya calendar"): The Maya calendar is a system of calendars used in pre-Columbian Mesoamerica and in many modern communities in the Guatemalan highlands, Veracruz, Oaxaca and Chiapas, Mexico.
Relevant evidence: Yes