Finding the Year’s Share in Day-of-Week Calculations

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Why is it important?

The dominant part in the mental calculation of the day of the week for any given date is to determine the "year share" (the contribution of the two-digit year part of the date). This paper describes a number of year share computation methods, some well-known and some new. The “Parity Minus 3” method, in particular, is a new alternative to the popular “Odd+11” method. The paper categorizes the methods of year share computation, and presents simpler proofs of their correctness than usually provided.