In 1582, Christopher Clavius and a council working at the direction of Gregory XIII (Pope of the Roman Catholic Church) completed a reconstruction of the Julian Calendar producing new Easter tables.The new calendar was issued in February in the papal bull called "Inter gravissimas".

The Council decided to keep Easter on the same Sunday throughout the Christian world.

To fix incontrovertibly the date for Easter, and to make it determinable indefinitely in advance, the Council constructed tables to compute the date.

Easter is an annual festival observed throughout the Christian world.

The date for Easter shifts every year within the Christian calendar.

For dates of Easter and other Christian observances, see the Selected Christian Observances service.

The lunar cycles used by the ecclesiastical system are simple to program.

The ecclesiastical rules are: Easter can never occur before March 22 or later than April 25.

The Gregorian dates for the ecclesiastical full moon are determined using the tables in the Papal bull Inter Gravissimas.

These tables were revised during the following few centuries resulting, eventually in the tables constructed by the 6th century Abbot of Scythia, Dionysius Exiguus.

Nonetheless, different means of calculations continued in use throughout the Christian world.

By the 1700's, though, most of western Europe had adopted the Gregorian Calendar.