A calendar function on a watch allows one to display the current date, occasionally, even with the day or month. It is quite a handy feature for those who sometimes want to know the details of the day without taking out their phone at that moment. Barely decorated date windows display the day. More sophisticated displays can be extended to fully display the moon's date, day, month, and even phases.
Calendar watches may be mechanical or automatic; furthermore, they are even programmed to adjust the calendar automatically for leap years. "A calendar on a watch is equivalent to having a mini organizer on your wrist, rather than just something carrying the time."
