According to Daniel Zwillinger (“Standard Mathematical Tables And Formulae”; 31st ed; 2003; Recipe 10.3.2, but formula 10.3.1) the specific date maps to the following day of the week (in the Gregorian calendar):
- W = day of the week (0=Sunday to 6=Saturday)
- k = the day in the month (= 1 to 31)
- m = the month (1=March to 12=February)
- C = century minus one (1997 , 2005 )
- Y = the year inside century, where the years begining is march 1st (so, 1997 maps to except for January and February when it goes to
- and is the floor function (the largest integer part of the enclosed real number).
For example, today is March 29th, 2011. That would be:
- The day’s order number inside this month:
- This month is, according to Roman counting, the first one in the year:
- The year inside the century is (since it is past February)
- The century is 21st, so
- So: , ,
- and i.e. today is Tuesday (correct).