The rules for counting significant figures can be stated as follows:

1] All non-zero digits are significant.

2] All zeroes between two non-zero digits are significant.

3] All zeroes to the left of the first non-zero digit are NOT significant.

4] All zeroes to the right of the last non-zero digit and to the left of an understood decimal point are NOT significant.

5] All zeroes to the right of the last non-zero digit where a decimal point is written are significant.

6] All digits in the coefficient of a number in scientific notation is significant.

7] When rounding a number which ends exactly with a five (5), then round the preceding digit to an even number. This means that if the number preceding the five is an odd number, it rounds up to the even number. or if the number preceding the five is an even number, it remains the same even number.

8] When adding or subtracting measurements, first round all the numbers to the same column as the least accurately measured value. Then add or subtract.

9] When multiplying or dividing measurements, do the calculation first. Then round the answer to the same number of significant digits as the original values with the fewest significant digits.