effective digit
From the first non-zero digit to the last digit on the left of a number, all digits are valid digits of this number.
It is from the first non-zero number on the left to the last number. All numbers (including 0, excluding the n power of 10 in scientific notation) are called effective numbers. In short, all zeros before a number are deleted, and everything from the first positive integer to the exact number is a valid number.
For example: 0.0 109, the first two zeros are not significant numbers, and the following 109 is significant numbers (note that the middle zeros are also counted).
In 3. 109 * 105 (3. 109 times10 to the fifth power), 3,109 are all significant numbers, and the fifth power of10 is not.
5.2 * 10 6, only 5 and 2 are valid figures.
0.0230, the first two zeros are not significant numbers, and the last 230 are significant numbers (the last two zeros are also counted).
1.20 has three significant figures.
1 100. 120 has 7 significant digits.
In 2.998 * 10 4 (2.998 multiplied by the fourth power of 10), three significant digits are reserved as 3.00 * 10 4.
The significant digits of logarithm are all digits after decimal point, such as log x= 1.23, log a=2.045, 0, 4.5, and pH=2.35, 3.5.