The method of finding the divisor is called rounding method. Whether it is "rounding" or "entering" depends on whether the number in the highest digit of the omitted mantissa is less than 5 or equal to or greater than 5.

When taking decimal approximation, if the highest digit of mantissa is 4 or less, the mantissa is removed. If the highest digit of mantissa is 5 or more, the mantissa is rounded and "1" is input before it, which is called rounding method.

Rounding is an accurate counting reservation method, which is essentially the same as other methods. But the special point is that rounding can make the difference between the reserved part and the actual value not more than half of the last order of magnitude.

If the probability of 0 ~ 9 is equal, the error sum of this method is the smallest for a large number of reserved data. This is why we use this method as the basic booking method.

Development history:

In 527 AD, when the astronomer monk and his party in the Tang Dynasty compiled the Great Liyan Method, after careful study, they found that the apparent speed of the sun on the ecliptic was not uniform, but fast and slow, with the fastest speed in winter and then slow down. The average speed was at the vernal equinox, the slowest in summer and the opposite in summer. According to this principle, he divided the year into four sections, from the autumnal equinox to the winter solstice, and from the winter solstice to the vernal equinox, totaling 88.89 days.

From vernal equinox to summer solstice, from summer solstice to autumn equinox is 93.75 days. When calculating the longitude of the sun, because the time between two solar terms is a variable, he created the independent variable "quadratic internal manipulation formula with unequal time interval" Using this formula, the calculation result is more accurate.