Proleptic Gregorian calendar Proleptic Gregorian calendar The proleptic Gregorian calendar is produced by extending the Gregorian calendar backward to dates preceding its official introduction in 1582. In countries that adopted the Gregorian calendar later, dates occurring in the interim (between 1582 and the local adoption) are sometimes "Gregorianized" as well. For example, George Washington was born on February 11, 1731 (Old Style), as Great Britain and its possessions were using the Julian calendar with English years starting on March 25 until September 1752. After the switch, that day became February 22, 1732, which is the date commonly given as Washington's birthday. The proleptic
Decimal calendar calendar. It consisted of twelve months, each divided into three "décades" of ten days, with five or six intercalary days called "sansculottides". The calendar was abolished by Napoleon on January 1, 1806. The modern Gregorian calendar does not use decimal units of time, however several proposed calendar systems do. None of these have achieved widespread use. Decimal calendar A decimal calendar is a calendar which includes units of time based on the decimal system. The original Roman calendar consisted of ten months (however, the calendar year only lasted 304 days, with 61 days during winter not assigned to any month).