Faults in the Gregorian calendar
The numbering of the calendar weeks represents another problem with the week. The first week in the year is not always the calendar week "one"!
The average man in the street who doesn’t have to tackle the subject, will not immediately understand why there is any problem. He believes that week number one is actually the first week in the year.
Everyone can instantly understand that a week which begins with a Saturday can actually not be a "real" week. Therefore an international agreement must exist governing as of which day a week can be counted as a full one. As tricky and as harmless as this question is can be seen from the original text from the German Standards Committee in its standards specifications paper DIN 1355 "Time". It is worded as follows:
The first calendar week of a calendar year is that which includes the first Thursday of the calendar year and therefore belongs to the beginning year by more than half".
This regulation however had to be revised. The standards specifications paper DIN 1355 "Time" was replaced by the ISO 8601.
For example, the count of calendar weeks deviates by one in the USA in 1999 and 2010.