About perpetual calendars
A perpetual calendar is a calendar display mechanism that allows you to check the date, day of the week, month, and other calendar information in addition to the time, and can automatically adjust and display months with 30 or 30 days.
A calendar year is calculated as 365.425 days, and a leap year is established every four years to correct this error. However, a perpetual calendar can adjust for leap years and can display the number of days in a month as 30, 31, 28, or 29, so manual correction is not necessary.
The first to be equipped was a pocket watch, but as the demand for wristwatches increased, development was carried out to install a perpetual calendar mechanism on wristwatches, and in 1925, the first wristwatch with a perpetual calendar was produced by Patek Philippe in history.
