Yesterday I attended a training session on the workings of the immigration/asylum system in the UK. I heard that one chap, who claimed at his hearing to be a Christian, was asked to prove it by a) naming the date for Easter next year* and b) describing how to cook a turkey. Another chap's claim to have been tortured was turned down because he couldn't state the colour of the torturer's tie. His explanation that his mind was filled with other things at the time was not accepted.
*Had this unfortunate person been, like me, a choirboy in his youth, and whiled away the sermons by flicking through the Book of Common Prayer, he would have known that the date for Easter (the Sunday following the first full moon after the Vernal Equinox) can be found using the Golden Number and the Sunday Letter.
To find the Golden Number, add One to the Year of our Lord, and then divide it by 19; the remainder, if any, is the Golden Number; but if nothing remaineth, then 19 is the Golden Number.
To find the Sunday Letter, add to the Year of our Lord its fourth part, omitting fractions, and also the number six: divide the sum by seven; and if there is no remainder, then A is the Sunday Letter: but if any number remaineth, then the letter standing against that number in the small annexed table (below), is the Sunday Letter.
Or he could buy a diary.
But if he were an Orthodox Christian it would be different.