It's easier for you to calculate this way: 365 days, 5 hours, 48 minutes and 46 seconds = 365.24 19 days, so the current calendar stipulates that leap years are every 4 years 1 leap, every 1 leap every 00 years, and then every 400 years 1 leap. This is 0.242 19*4=0.96876 days, which is close to 1 day, so it is 1 leap, but every four years it is1-0.96876 = 0.03124 days, too. But it will lose 1-0.781= 0.219 days every 100 years, so it will lose 0.2 19*4=0.876 days every 400 years, so it will increase/every 400 years. So every 400 years plus 1-0.876=0. 124 days, 1/0. 124 is about 8,8 * 400 = 3200 years. In other words, this calendar will increase by 1 day every 3200 years. Then do the corresponding treatment, not to mention 3200 years is already a long time.

Whether you add 1 leap or subtract 1 leap, it is reflected in February. As long as it is a leap year, February is 29 days. As long as it is not a leap year, February is 28 days. As for why February was chosen, it is related to the history of this calendar. This calendar originated in the Roman Empire. In ancient Rome, February was the month of executing prisoners every year, so people wanted this month to be shorter, so only February was the shortest. It is also related to Augustus Octavian, the heir of Julius Caesar. Originally 1 October1,3, 5, 7, 9,1day, April 30th, June 8th, 10, 12, February 29th. In order to show his greatness, Augustus Octavian took out February of 1 day and put it in August when he was born, and adjusted the following months accordingly, naming August after Augustus. This is today's calendar.

As for whether we have caught up with "every 100 1 leap, and then every 400 1 leap", 2000 is an integer multiple of 400, which is a leap year, and we have caught up. However, 1900 and 2 100 are not integer multiples of 400, nor are they leap years.