There are different ways that the calendar is being displayed in the watch’s dial. The usual date display shows the day of the month either digital or manual. There are also other watches that display the full calendar data such as the day, month, year, as well as the day of the week. There are automatic and manual timepieces; automatic timepieces automatically adjust conforming to the number of days a month have while the manual ones need to be manually adjusted. There are also annual calendars and perpetual calendars. Annual calendars are automatic and perpetual calendars are manually corrected.
The two types of gear train, which are the reducing gear train and the multiplying gear train, operates the calendar complication and the watch escapement respectively. The reducing gear train which is significant in the calendar complication is located on the dial part of the movement.
The date train is driven by the hour wheel. The hour wheel plays an important role in the motion works. It controls the rotation of the hands both of the hour and minutes. For watches that displays 12 hours, the hour wheel will rotate once in 12 hours. Watches with 12 hour display have a ratio setting that drives the date disc driving wheel. In this matter, the ratio is 1:2 after 12 hours. For 24 hour display, the ratio is 1:1 after 24 hours. The date disc is being controlled by the one tooth gear mounted co-axially that the date disc driving wheel has. There are 31 interior teeth in a date disc that is hidden by the dial. This is how the date display changes every after 24hours.
Watches that indicate the day of the week also have 7 teeth under the dial. It works just like the day of the month display. The disc will rotate after 24 hours.
Lastly is the month indicator. The month indicator adjusts through its date disc driving wheel that rotates in every 24 hours. The intermediate month disc driving wheel contains 31 teeth signifying 31 days. There are 31 teeth since most months have 31 days. It has fingers that drive this wheel.
On the other hand, the month disc also has 12 teeth representing every month of the year.
To assure that the discs that control the date, day, and month are not driven unintended, there are jumping springs that keep them in place. This will lessen the impact of shock to the discs. Disc movement is being prevented because only the torque of the driving wheel can overcome the jumper spring. This will assure that they are only driven intentionally.