Leap week calendar week calendars would synchronize with the Gregorian every 400 years Note that the new years of the calendars shown need not be synchronised. The years according to ISO week date applied to months, i.e. a month has as many weeks as it has Thursdays, are shown depending on the weekday of 1 January, shaded weeks belong to the month they are labeled with in regular years and to the other adjoining one in leap years. Leap week calendar A leap week calendar is a calendar system with a whole number of weeks every year, and with every year starting on
Armelin's calendar Armelin's calendar Armelin's calendar was developed around 1887 by French astronomer Gustave Armelin, who developed a twelve-month calendar in which the year of 364 days was divided into four equal quarters of 91 days. Armelin's calendar proposal was discussed chiefly under the auspices of the Société astronomique de France in 1887 and recently in the French Academy of Sciences. The advantages of this simple system are evident. The months are nearly equal in length, and all have the same number of business days. Any given day of any month falls on the same day of the week each year. A