Significant Figures and Rounding Off Numbers Significant figures are digits in a measurement that are known with greater certainty than the digits that are l...
Significant figures are digits in a measurement that are known with greater certainty than the digits that are less certain. They are used to express the accuracy and precision of a measurement.
How to identify significant figures:
Start from the left to the right in the measurement.
Count the number of significant figures (SFs) in each place value.
The SFs of each place value are determined by the uncertainty of that digit.
For example, the uncertainty of the first digit in the measurement is usually one SF. The uncertainty of the third digit is usually two SFs, and so on.
Only count the SFs in the digits that are known with certainty.
Examples:
5.03 has 2 SFs.
12.00 has 1 SF.
0.0012 has 2 SFs.
Rounding off numbers:
Round off the number to the closest whole number or digit in each place value.
Pay attention to the last digit. If the last digit is 5 or greater, round up. If it is less than 5, round down.
Rounding can sometimes change the value of the measurement.
Example:
Rounding 5.03 to the nearest whole number gives 5.
Rounding 12.00 to the nearest whole number gives 12.
Rounding 0.0012 to the nearest hundredth gives 0.01.
Important note:
Significant figures and rounding are not the same thing. Significant figures tell us how many digits are known with certainty, while rounding tells us how many digits are significant in the final measurement