Term: Byzantine calendar, Description: The calendar used by the Eastern Orthodox Church from c. 691 to 1728, Question: Did Ivan the Terrible use the Byzantine calendar?, Answer:Yes
Fact1: Ivan the Terrible was the Tsar of Russia from 1530 to 1585.  Fact2: The Byzantine calendar was the official calendar of the Russian government from 988 to 1700. Fact3: The Tsar was the leader of the Russian government.  