Leap Year: How the World Makes Up for Lost Time.
The problem as it turned out was the Julian calendar. It didn't calculate leap years very well and was putting more in than was required. So a new calendar.

leap year calendar

leap year calendar

Gregorian calendar - Simple English Wikipedia, the free encyclopedia.

The Galileo Project | Chronology | Gregorian Calendar.

The Gregorian calendar, which now serves as the standard calendar for civil use throughout the world, has both common years and leap years. A common year.
The Gregorian calendar is a modified version of the Julian calendar. The only difference being the specification of leap years. The Julian calendar specifies that.
Why do we have leap years? - Canada - CBC News.

Calendar's Quirk Can Pose a Payroll Challenge.
The Gregorian calendar, which now serves as the standard calendar for civil use throughout the world, has both common years and leap years. A common year.
Is It Time to Overhaul the Calendar?: Scientific American.

Leap Year -29 February 2012.

EXACT DAYS-1N-A-YEAR CALENDAR (EXCLUDING LEAP YEAR). Day of 31 28 31 30 31 30 31 31 30 31 30 31 month Jan. Feb. Mar. Apr. May June July Aug.