From the Introduction to the Wikipedia article titled Determination of the day of the week:

The basic approach of nearly all of the methods to calculate the 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.

In reply to Re: Gettting the last Friday of every month using Time::Piece by Jim
in thread Gettting the last Friday of every month using Time::Piece by Anonymous Monk

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