All the digits in a measurement, including the uncertain last digit, are called significant figures or significant digits. Note that zero may be a measured value; for example, if a scale that shows weight to the nearest pound reads “140,” then the 1 (hundreds), 4 (tens), and 0 (ones) are all significant (measured) values.
A measurement result is properly reported when its significant digits accurately represent the certainty of the measurement process. Below are a set of rules to determine the number of significant figures in a measurement:
Uncertainty in measurements can be avoided by reporting the results of calculation with the correct number of significant figures. This can be determined by the following the rules for rounding numbers:
An important note is that rounding of significant figures should preferably be done at the end of a multistep calculation to avoid the accumulation of errors at each step due to rounding. Thus, significant figures and rounding, facilitate correct representation of the certainty of the measured values reported.
This text is adapted from Openstax, Chemistry 2e, Section 1.5: Measurement Uncertainty, Accuracy, and Precision.