Rounding is an accurate counting retention 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 exceed half of the last order of magnitude. If there is a probability of 0 ~ 9, the total error of this retention method is the smallest for a large number of retained data. This is probably why we regard this method as the basic reservation method.

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About equal means about how much, which is an estimate, calculated according to the rounding algorithm.

Usually tell the exact number of digits. If it is accurate to ten digits, 49 1 is about 490. According to the rounding algorithm, if the number on a number is below 4, such as 362, it is about 360, and if the number on a number is above 5, such as 287, it is about 290.