1, if a number can accurately represent a certain quantity, then this number is called the exact number of the quantity;

2. The number used to represent the exact value of the quantity is called the exact number;

3. The value close to the exact value is called approximation. The approximation with smaller accurate value is called insufficient approximation, and the approximation with larger accurate value is called excessive approximation.

Extended data:

The difference between approximate value and exact value is called error. According to the source of error, error can be divided into measurement error, truncation error and Scheeren error.

An accurate number refers to a number without error. If the side length of a square is a, its circumference is 4a. Where 4 is an exact number, there is no mistake. Exact numbers are usually expressed as integers or fractions, but exact numbers can also be expressed as decimals or irrational numbers. For example, 1mm=0.00 1m, where 0.00 1 is an exact number. The circumference of a circle with a diameter d is πD, and the diagonal length of a square with a side length a is the root number 2a.

Baidu Encyclopedia-Accurate Numbers