Rules for determining significant figures

1. All nonzero digits are significant.

2. All zeroes between nonzero digits are significant.

3. Zeroes to the right of a nonzero digit, but to the left of an understood

   decimal point, are not significant. 

        If such zeroes are known to have been measured, however, they are  

   significant and should be specified as such by inserting a decimal point to the

   right of the last zero.

4. In numbers less than one, zeroes to the right of a decimal point that are

   to the left of the first nonzero digit are never significant. 

   They are simply placeholders.

5. In numbers less than one, the zero to the left of the decimal point is

   never significant.

6. All zeroes to the right of a decimal point and to the right of a nonzero

   digit are significant.

 

Addition and Subtraction Involving Significant Figures

In addition or subtraction, the arithmetic result should be rounded off so that the final digit is in the same place as the leftmost uncertain digit.

Multiplication & Division Involving Significant Figures

The arithmetic product or quotient should be rounded off to the same number of significant figures as in the measurement with the fewest significant figures.