Significant figures, also known as significant digits, are the number of digits in a given value or measurement that contribute to the degree of accuracy of the value. They are important in scientific or technical measurements, where precision is crucial. The idea behind significant figures is to ensure that the result of a computation is not more precise than the things that were actually measured to obtain that result.

Here are some rules for determining the number of significant figures:

• All non-zero digits are significant. For example, the number 652.1 miles has 4 significant figures.
• All zeros in between non-zero digits are significant. For example, the number 23.0041 has 6 significant figures.
• Zeros on the right of a decimal point and before (or to the left of) the first non-zero digit are not significant. They only represent the position of the decimal point. For example, the number 0.003 has 1 significant digit.

Significant figures are counted starting from the first non-zero digit of a number, which is called the first significant figure. The next digit is then called the second significant figure, and so on. A significant figure could be to the left or right of the decimal point.

In summary, significant figures are a way to determine the accuracy and precision of a measurement or value. They are important in scientific or technical measurements, and there are rules for determining the number of significant figures.