Calendar mechanism

A calendar mechanism for a timepiece comprising a date display with date-discs, a date programme unit arranged to drive the date-discs, a drive unit arranged to drive the date programme unit and a drive member of the timepiece arranged to actuate the drive unit, wherein the date-discs comprise a first lower units disc and a second upper units disc, which are superposed and free to rotate with respect to each other and a third lower tens disc and a fourth upper tens disc, which are superposed and free to rotate with respect to each other, the first lower units disc being divided into eight sectors occupied by the numerals 8, 9, 0 and 1, the second upper units disc being divided into eight sectors, of which seven sectors are occupied by the numerals from 1 to 7 and one sector is occupied by an aperture revealing one of the numerals borne by the first lower units disc, the third lower tens disc being divided into eight sectors occupied by the numerals 2 and 3, the fourth upper tens disc being divided into eight sectors, of which seven sectors are occupied by the numerals 0, 1 and 2, and one sector is occupied by an aperture revealing one of the numerals borne by the third lower tens disc, and wherein the date programme unit comprises a first date programme wheel set for actuating the first lower units disc and the third lower tens disc, and a second date programme wheel set for actuating the second upper units disc and the fourth upper tens disc, said first and second date programme wheel sets being arranged to mesh selectively with the date-discs so that the last day of the month is displayed with the third lower tens disc and the first lower units disc and the first day of the following month is displayed with the fourth upper tens disc and the second upper units disc, the change of date between two consecutive months occurring via a single jump of the fourth upper tens disc and of the second upper units disc, regardless of the month.