Question: Did the Eastern Orthodox Church and the Byzantine Empire ever use the same calendar?, Answer:Yes, Description of Byzantine calendar: The calendar used by the Eastern Orthodox Church from c. 691 to 1728, Fact1: Eastern Orthodox Church used the Byzantine calendar from c. 691 to 1728, Fact2: The Byzantine Empire used the Byzantine calendar from c. 988 to 1453
Step1: What calendar did the Eastern Orthodox Church use from  c. 691 to 1728?, Step2: What calendar did the Byzantine Empire use from c. 988 to 1453?, Step3: Is #1 and #2 the same?, Wikipedia page for step 1: Eastern Orthodox Church, Wikipedia page for step 2: Byzantine Empire, Wikipedia page for step 3: , not_definitive_answer: False, incorrect_answer: False