AKA the Republican Calendar. Was officially adopted in France on October 24, 1793 and abolished on 1 January 1806 by Emperor Napoleon I.

It was used again briefly during under the Paris Commune in 1871. The French also established a new clock, in which the day was divided in ten hours of a hundred minutes of a hundred seconds - exactly 100,000 seconds per day.

As in most calendars, the year had 12 months - each one of 30 days. There were no weeks - instead each month was divided into three décades of 10 days, of which the final day was a day of rest. This was an attempt to de-Christianize the calendar, but it was an unpopular move, as it reduced the resting days from 1 out of 7 to 1 out of 10.

To compensate for the last 5.24 days of the year, five - sometimes six - additional days were put in the calendar at the end of the year (which was around the 22nd of September - or the 1st of Vendémiaire in Republican Calendar terms.)

As the calendar only lasted for about 14 years, there was only ever three leap years, where the sixth additional day - Revolution day - existed - in the years 3, 7 and 11.