The holiday should be after the Old Testament Easter.
The method of calculating Easter was very complicated, several cycles were taken as a basis, which were considered from the day the world was created (“Summer from Adam”). To find out what kind of “summer is from Adam” now, by the year of our era, you need to add number 5508. In 2014, we have 7522 years from creating the world. The next cycle that was needed to coordinate Easter is an indicator. Indicts are only 15. To calculate which indict is now, you need to divide the year from the creation of the world into 15 without fractional numbers. The remainder that turned out is the indict. That is, 7522 = 501*15+7. So 2014 is a year 7 indication.