Uncertainty in Measurement: Significant Figures

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.

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All of the numbers in a scientific measurement are certain, except for the last digit. The certainty of measurement depends on two factors: the number of digits in the measurement and the precision of the instrument used. 

In a measured quantity, all of the digits, including the last uncertain digit, are called significant figures&n...