What other term for dual dating?
Old Style (O.S.) and New Style (N.S.)
What dual dating for?
differences in the starting date of the year
How many years it is for?
two consecutive years
What name it has included?
Pope Gregory XIII,
In what year it changed?
in 1582
Why it has to change?
to bring the date for the celebration of Easter to the time of year in which it was celebrated when it was introduced by the early Church