What day of the week was February 14th, 1997? What day will be on June 10th, 2013? It will take a clever man to say that. And the 15th of the next month, or of the following month? Several operations of mental calculation are necessary to get to the end of this puzzle. Several operations, that is to say so many sources of error.

Here is indeed the paradox: a notion as usual as the date is an inextricable jungle.

Let us imagine for a moment that we count the time of the day as we count the time of the year. What would it give? We would have hours of unequal durations, 47 minutes, 53, 61, 67 — preferably prime numbers to prevent any subdivision. These hours would succeed one another according to a studied untidiness which we shall omit to detail here so as not to bore the reader. Result: a day would not be made up of an integer of hours, but of 23 hours and 28 minutes, 23 hours 54, 24 hours 17, 24 hours 26 or I don't know what else. One day later, we would not read the same hour, and we would succeed in finding a way in this maze only by means of printed tables. These tables would be called... calendars.

Do you smile? Please, look at a calendar. It is exactly that. The scale is there the year instead of the day. The principle is the same. Out of a cycle of forty-eight months there are three 28-day months, one 29-day month, sixteen 30-day months, twenty-eight 31-day months. Apart from three exceptions, the duration of the month is never in correlation with the one of the week. Why make it simple when you can make it complicated? Consequence: two consecutive years do not begin on the same day.

Because our spirit is accustomed to it since our youth, we no longer see the extravagance of this jumble. From further away the work falls us from hands. The only fact that we need a new calendar every year to get our bearings is in itself a piece of nonsense. Do we change our watch every day? Fortunately not. Let us see now how to tidy up this shambles.