Week for calculation of the Gregorian calendar date

Weekly computing availableZeller Formula(Applicable only after October 15, 1582 ):

W = Y + [Y/4] + [C/4]-2C + [26 (m + 1)/10] + D-1

The meanings of the symbols in the formula are as follows:
C: Century (double digits of the year );
Y: year (two digits below the year level );
M: Month (M is greater than or equal to 3, less than or equal to 14, that is, in the caile formula, the 1 and February of a year are regarded as the 13 and 14 months of the previous year.
For example, January 1, 2005 is regarded as the 13-month-1 day of 2004 );
D: Day;
[] Indicates an integer.
W: Week; W: 7: 0-Sunday, 1-Monday, 2-Tuesday, 3-Wednesday, 4-Thursday,
5-Friday, 6-Saturday

Take February 14, 2005 as an example: c = 20, y = 4, M = 14, D = 14
W = 4 + [4/4] + [20/4]-2*20 + [26*(14 + 1)/10] + 14-1
= 4 + 1 + 5-40 + 39 + 14-1
= 22 (divided by more than 7 1)
Therefore, July 22, February 14, 2005 is Monday.
The reason why Zeller's formula was only suitable for the situation after October 15, 1582 was that the Pope gregali 13th organized a group of astronomers in 1582, according to the computation of the godnex, made changes to the Confucianism. The revocation will be announced within 10 days from January 1, October 5-14, 1582, following January 1, October 4 as January 1, October 15.
Later, people referred to this new calendar as the "Gregorian Calendar", that is, the calendar commonly used in the world today, or the Gregorian calendar.