Determination of the day of the week determined for the latter part of the analysis. By using a given day August 13, 2009 which was a Thursday as a reference, with "Base" and "n" being the number of days and weeks it has been since 01/01/0001 to the given day, respectively and "k" the day into the given week which must be less than 7, "Base" is expressed as Knowing that a year divisible by 4 or 400 is a leap year while a year divisible by 100 and not 400 is not a leap year, a software program can be written to find the number of
Determination of the day of the week since the start of the century, and then add these together along with the number of years since the start of the century, and the day number of the month. Eventually, one ends up with a day-count to which one applies modulo 7 to determine the day of the week of the date. Some methods do all the additions first and then cast out sevens, whereas others cast them out at each step, as in Lewis Carroll's method. Either way is quite viable: the former is easier for calculators and computer programs; the latter for mental calculation (it is quite