1. All non-zero numbers are significant.
Example: 43.56721 has seven significant figures.
.................21 has 2 significant figures.
................1234.56789 has 9 significant figures.

2. Zeros appearing between non-zero figures are significant.
Example: 80.46 has four significant figures.
................12,007.002 has eight significant figures.

3. Zeros that appear in front of non-zero figures are NOT significant.
Example: 0.006732 has four significant figures.
................0.00000003 has one significant figure.

4. Zeros at the end of a number and to the right of a decimal are significant.
Example: 68.000 has five significant figures.
................12.00000000 has ten significant figures.

5. Zeros at the end of a number but to the left of the decimal may or may not be significant. If a number has a decimal at the end, all numbers are significant. If no decimal is written, the zeros on the end are place holders and should not be considered significant.
Example: 2000 contains one significant figure.
................2000. contains four significant figures.