Due to its development the Gregorian Calendar is irregular.
- The start date corresponds to the wrongly dated the birth of Christ. Divide the story in an event relevant only for a fraction of humanity.
- Don't have year 0.
The duration of the months in the quarters is different as well as the duration of the quarters.
Quarter 1: 31, 28/29, 31. Total 90/91
Quarter 2: 30, 31, 30. Total 91
Quarter 3: 31, 31, 30. Total 92
Quarter 4: 31, 30, 31. Total 92
The leap day location at second month end causes the displacement of a date on the day of the week is different if the date is before or after February 29. If before, the double displacement occurs on the year after the leap year. If after, the double displacement occurs on the same leap year.
2011 2012 2013 January, 1 Saturday Sunday Tuesday March, 1 Tuesday Thursday Friday
The Gregorian Calendar is associated with beliefs shared only by a segment of the humanity.
Displacement of dates on the day of the week
Supporters of perpetual calendars proposals considered a deficiency of Gregorian Calendar that every year starts at a different day of the week. I disagree. The day of the week rotation in which year begins leads to the displacement of dates on the day of the week, so celebrations, holidays and birthdays vary their position in the week. It would be extremely sad that birthday were always, by example, on Monday.