The French revolutionary calendar was officially in use from 24 October 1793 to 1 January 1806, when it was abolished by Napoleon I. By 1795 it was no longer compulsory to use decimal (revolutionary) time and a number of clocks were made which employed both systems, as on the present example.
The revolutionary day was divided into ten hours of one hundred minutes (with one hundred seconds). The week was dispensed with and each month of thirty days was divided into three décades, leaving 5 or 6 holidays at the end of the year.
The names of the décades were called in straightforward fashion: primidi, duodi, tridi, quartidi, quintidi, sextidi, septidi, octidi, nonodi, decadi. The names of the months were rather more poetic, reflecting the attributes of the time of year: Vendèmiaire, Brumaire, Frimaire, Nivose, Pluviose, Ventose, Germinal, Florèal, Prairial, Messidor, Thermidor and Fructidor. The dish 'lobster thermidor' comes from the eleventh month of the revolutionary calendar.