Significant figures are critical when reporting scientific data because they give the reader an idea of how well you could actually measure/report your data. Before looking at a few examples, let's summarize the rules for significant figures.

- 1) ALL non-zero numbers (1,2,3,4,5,6,7,8,9) are ALWAYS significant.

- 2) ALL zeroes between non-zero numbers are ALWAYS significant.

- 3) ALL zeroes which are SIMULTANEOUSLY to the right of the decimal point AND at
the end of the number are ALWAYS significant.

- 4) ALL zeroes which are to the left of a written decimal point and are in a number >= 10
are ALWAYS significant.

Examples: How many significant figures are present in the following numbers?

Number | # Significant Figures | Rule(s) |

48,923 | 5 | 1 |

3.967 | 4 | 1 |

900.06 | 5 | 1,2,4 |

0.0004 (= 4 E-4) | 1 | 1,4 |

8.1000 | 5 | 1,3 |

501.040 | 6 | 1,2,3,4 |

3,000,000 (= 3 E+6) | 1 | 1 |

10.0 (= 1.00 E+1) | 3 | 1,3,4 |

This gives you some idea of how to determine the number of significant figures in a single number. To find out how to use this information when performing mathematical operations (addition, subtraction, multiplication, division), see "Significant Figures: Mathematical Operations."

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