This day is designated the first day of the month of Vend miaire in year 1 of the Republic. Subsequent years begin on the day in which the September equinox occurs as reckoned at the Paris meridian.
Days begin at true solar midnight.
Whether the sans-culottides period contains five or six days depends on the actual date of the equinox. The calendar therefore stays perfectly aligned with the seasons. No attempt is made to synchronise months with the phases of the Moon. The Republican calendar is rare in that it has no concept of a seven day week. Each thirty day month is divided into three d cades of ten days each, the last of which, d cadi , was the day of rest.