Numbers begin with the first number on the left that is not 0, and all subsequent numbers are valid. For example, the significant number of 0.000 10 1 is 1, 0, 1 is three, and the significant number of 0. 123 123 is 1, 2, 3, 3.

Effective number refers to the number that can actually be measured in the analysis work. In mathematics, significant digit refers to the number of digits in a number from the first non-zero digit to the last digit. For example, 0.6 18 has three significant figures, namely 6, 1 8.

The last digit of the significant figure is an estimate, which is uncertain. Generally, only one significant bit of uncertainty is taken, and its number is the position of the suspicious bit of the measurement result. Its last digit corresponds to the position of the suspicious digit of the measurement result.

Since the last digit of the significant figure is where the uncertainty lies, the significant figure reflects the uncertainty (or error limit) of the measured value to some extent. The more significant digits of the measured value, the smaller the relative uncertainty of measurement; The fewer significant figures, the greater the relative uncertainty. It can be seen that effective figures can roughly reflect the uncertainty of measurement results.