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Scientists know that their results always contain errors  Significant digits is one way of keeping track of how much error there is in a measurement.  The basic idea behind significant digits is to show the amount of accuracy and precision in experimental results without doing a lot of statistical analysis.  They should be properly used in calculations for all experimental work.

Since significant figures are a method of keeping track of the amount of error in experimental results, they only apply to experimental measurements.  Some numbers are exact, and are not affected by the number of significant digits.

Significant digits aren't the only, and are not the best, way of keeping track of errors in experimental data, but they are often used in beginning science classes.  Don't get hung up on the rules for significant digits. They are only a crude tool for showing the approximate amount of error in a measurement or calculated result.  Use the rules with good judgment, rather than following them rigidly at all times.

Results of a calculation that involves experimental results – whether addition, subtraction, multiplication or division – should generally be reported using significant digits.

You won't get much out of these pages if you just read them! As you go along you'll see a number of questions in boxes like this.  Work them out and check them as you go along, to make sure you understand what you have just read.

More advanced topics are indicated with this symbol.

There is a section quiz for each of the main topics in this tutorial.  Make sure you try each of them to see if you have the right concepts.  Finally, at the end take the summary test.