Computus

Computus (Latin for "computation") is the method for calculating the date of Easter. In the early 4th century there was confusion about when Christian Easter or the Resurrection should be celebrated.
History.
Background.
At the Arles Council, in 314, was obliged to all the Christianity to celebrate Easter the same day, and that this date was going to be assigned by the Pope, that was going to send epistles to all the churches in the world with the necessary instructions. However, not all the congregations followed those precepts.
Nicaea Council.
In the First Council of Nicaea, in 325, this subject was solved.
Was established that the Resurrection Easter had to be celebrated fulfilling some norms:
However, there still were discussions between the Roman Church and the Alexandrian Church, while the Nicaea Council said that the Alexandria Church was right, they had to calculate the date (in Alexandria), then communicate it to Rome. The Roman Church had to spread the "computus" to the rest of the Christianity.
Calculation.
Let's define 5 variables, "a", "b", "c", "d", and "e". In addition to two constants, "M" and "N", so the years between 1900 and 2100 take the values 24 and 5, respectively. We'll call "A" the year that we want to calculate the Easter date.
If "d" + "e" &lt; 10, the Easter date will be in March ("d" + "e" + 22). If opposed ("d" + "e" &gt; 9), will be in April ("d" + "e" − 9).
There are 2 exceptions:
The values for M and N for years before 1900 or after 2100 can be obtained from the following table: