What is a perpetual calendar watch?

Why is there a perpetual calendar? To put it simply, if there is no leap year, there will be no birth of a perpetual calendar.

        To put it simply, the earth's orbit around the sun is not 365 days that we routinely understand, but 365 days of 5 hours, 48 minutes and 46 seconds. For the sake of good memory, it is called 365 days, and the extra 5 hours, 48 minutes and 46 seconds cannot. It disappeared out of thin air (that doesn't fit the logic of the Earth's people), so the earth-goers who are good at calculations started: every year, four years is 366 days of leap years, and the day of supplementation is more than that of more than five hours, so each It’s only a hundred years since I came to a leap year (I don’t know if it’s true that I can count the space), so in 2000 it was 366 days, and 400 years later, 2400 years in February also had 29 days.