What calendar did the Eastern Orthodox Church use from  c. 691 to 1728? What calendar did the Byzantine Empire use from c. 988 to 1453? Is #1 and #2 the same?
Byzantine calendar
Eastern Orthodox Church used the Byzantine calendar from c. 691 to 1728 The Byzantine Empire used the Byzantine calendar from c. 988 to 1453
The calendar used by the Eastern Orthodox Church from c. 691 to 1728
Did the Eastern Orthodox Church and the Byzantine Empire ever use the same calendar?