Tutorial on the Use of Significant Figures

All measurements are approximations--no measuring device can give perfect measurements without experimental uncertainty. By convention, a mass measured to 13.2 g is said to have an absolute uncertainty of 0.1 g and is said to have been measured to the nearest 0.1 g. In other words, we are somewhat uncertain about that last digit —it could be a "2"; then again, it could be a "1" or a "3". A mass of 13.20 g indicates an absolute uncertainty of 0.01 g.

The objectives of this tutorial are:

—Explain the concept of signficant figures.
—Define rules for deciding the number of significant figures in
   a measured quantity.
—Explain the concept of an exact number.
—Define rules for determining the number of significant figures in
   a number calculated as a result of a mathematical operation.
—Explain rules for rounding numbers.
—Present guidelines for using a calculator.
—Provide some exercises to test your skill at significant figures.

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