In chemistry, you are often asked to express numbers to either three or four significant figures. The word significant means to 'have meaning'. A number that is expressed in significant figures will only have digits that are imporatnt to the number's precision.

It is important to record your data and your answers to calculations to a reasonable number of significant figures. Too many and your answer is claiming an accuracy that it does not have, too few and you're not showing precision and care required in scientific analysis.

For example, 6.9301 becomes 6.93 if written to three significant figures.

Likewise, 0.00043456 is 0.00043 to three significant figures.

Notice that the zeros before the figure are not significant - they just show you how large the number is by the position of the decimal point. Here, a 5 follows the last significant digit, so just s with decimals, it must be rounded up.

Any zeros between the other significant figures are significant. For example, 0.003018 is 0.00302 to three significant figures.

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