Results are generally reported with one uncertain significant figure (usually +/-1). Example: reporting a mass of 12.554 g indicates that the experimenter is certain that the true mass lies in the range 12.553 - 12.555 g. If the uncertainty in the last significant figure is greater than +/- 1 it should be written explicitly: 12.554 g +/- 0.003 g.
addition and subtraction
The answer must be truncated to the same least significant decimal place as the number with the least significant figure from the right.
multiplication and division
The answer has the same number of significant figures as the factor with the smallest number of significant figures.
8.9 g / 12.01 g/mol = 0.74 mol
It is common to carry one additional significant figure through extended calculations and to round off the final answer at the end.
Copyright © 2000 by Brian M. Tissue, all rights reserved.