Question: How long and in what capacity did Joachim Rittstieg study a system of calenders used in pre-Columbian Mesoamerica?
Sentence (from "Joachim Rittstieg"): Joachim Rittstieg (born February 23, 1937 in Berlin, died May 27, 2014 in Rendsburg) was a secondary school mathematics teacher who had travelled in Mexico, Guatemala, Belize, Honduras and El Salvador, and had studied the Mayan calendar system as a 40-year hobby.
Relevant evidence: Yes