This is defined as a watch which, in addition to the date, also provides information about the day of the week, the month and often, but not always, the phases of the moon. The discs visible under the windows on the dial or the hands in the subdials, except for the month function, are connected to a wheel which makes one revolution in 24 hours and which, at midnight, drives all the wheels connected to the discs or hands, causing the latter to move one step forward. A movement equipped with a complete calendar, therefore, will always mark the 31st day at the end of the month and only by manual correction can the correctness of the information be restored in months with 30 or fewer days. Again manually, one must then intervene on the passage of the month, which only in rare cases is automatically triggered on the 31st day. In order to facilitate these manual corrections, there are small buttons on the side of the carrure which, with the help of levers, act directly on the wheels governing the individual pieces of information, thus enabling them to be changed independently, when they are all triggered at midnight. It is a good idea, however, to act on these little buttons when the marked time is not between 9 p.m. and 3 a.m., precisely when the gears are engaged to change the information. Usually the complete calendar module is designed and manufactured separately, and can be added to practically any pre-existing movement, as long as it comes with a date display.
