Significant figures

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Significant figures.


With thanks to Professor Webster.

The number of significant figures in a result is the number of figures that are reliably known. As an example, measure the diameter of the top of a coffee cup with a millimeter scale ruler. Observe the top is between 80 and 81 mm wide. That is two significant figures. By observing carefully, it might be judged to be between 80 mm and 80.5 mm. The observer could not use the ruler to write 80.23761 mm because that would mean a distinction with respect to 80.23762 mm.

Suppose that diameter is used in some calculations. The calculator displays perhaps ten digits. Please resist the temptation to write them all down. They are not meaningful since the input data are not known that well.

Set up your calculator or computer software to display an appropriate number of significant figures.

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