Introduction - If you have any usage issues, please Google them yourself
Of the problem: the structure of the calendar every 400 years is a big cycle, that is, this year' s month, day, week and 400 a few years ago, exactly the same. Existing astronomical calendar to run in accordance with the laws of celestial bodies, 365.2425 days a year access. In this way, every 400 years a total of 365.2425 × 400 = 146097 days. As if 365 days a year, every 400 years less 0.2425 × 400 = 97 days. This is a leap year 97 days depends on the set (366 a year) days to put together, so every 400 years a leap to set up 97