Adding a calendar mechanism to a standard watch movement creates a **calendar watch**, one of the more complex functionalitie

Adding a calendar mechanism to a standard watch movement creates a **calendar watch**, one of the more complex functionalities in horology. These watches display various traditional calendar information, such as date, day, month, and year. While we often encounter watches with calendar displays in daily life, it’s important to note that there are different types of calendar watches, each with varying degrees of complexity.

The most straightforward and commonly seen type is the **simple calendar watch**. These are prevalent in everyday settings, featuring either pointer-style or window-style displays for the date. Pointer-style uses hands to indicate the date, with large outer circle pointers or smaller sub-dial pointers, while window-style may include single or double windows for clarity, though some lower-end models might mistakenly display non-existent dates like ’39’.

**Annual calendars** represent the first step towards automated calendar calculation, showing the week, date, and month. They can differentiate between 30-day and 31-day months, with manual adjustments required only once a year during the transition from February to March. However, they do not account for leap years.

To address this, watchmakers developed the **perpetual calendar**, a more complex mechanism that can identify leap years and adjust accordingly, often featuring leap year displays. These watches consider month variations, including leap years, up to the year 2100 (a centennial year not divisible by 400). True perpetual calendars, which require no adjustments for 100 and 400 years, are rare mechanical marvels, epitomizing the pinnacle of horological craftsmanship.