Determination of the day of the week day of the week begins by starting from an ‘anchor date’: a known pair (such as January 1, 1800 as a Wednesday), determining the number of days between the known day and the day that you are trying to determine, and using arithmetic modulo 7 to find a new numerical day of the week. One standard approach is to look up (or calculate, using a known rule) the value of the first day of the week of a given century, look up (or calculate, using a method of congruence) an adjustment for the month, calculate the number of leap years
Week an early continuous use of a seven-day week; referring to the Jews during the Babylonian Captivity in the 6th century BC, after the destruction of the Temple of Solomon. While the seven-day week in Judaism is tied to Creation account in the Book of Genesis in the Hebrew Bible (where God creates the heavens and the earth in six days and rests on the seventh; , in the Book of Exodus, the fourth of the Ten Commandments is to rest on the seventh day, "Shabbat", which can be seen as implying a socially instituted seven-day week), it is not clear