Finding the divisor of a number depends on whether the number with the first digit from the left of the mantissa is greater than or equal to 5. If it is less than 5, all mantissas are discarded; If it exceeds 5, after rounding the mantissa, add 1 to its previous digit.

This method of finding approximate value is called rounding.

When calculating the surface areas of iron drums and buckets. The rounding method cannot be used for approximation. Because in practice, more materials are used than the calculated results. Therefore, if you want to keep the whole ten, the whole hundred square centimeters, decimeters, meters, etc. When you want to omit the unit, the tenth, the hundredth, etc. , even if it is below 4, go forward 1. This approximate method is called one-step method.

The difference between rounding method and one method is that rounding method is used to calculate the approximate number of integers, and 1 method is used to calculate the surface area of actual iron drums and buckets.