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Significant Figures


Significant digits may be identified as follows:

1.  All non-zero digits are significant.

Example:
  • '987.65' has five significant figures: 9, 8, 7, 6, and 5.

2.  Zeros appearing in between two non-zero digits are significant.

Example:

  • '705.24' has five significant figures: 7, 0, 5, 2, and 4
3.  All zeros appearing to the right of an understood decimal point or zeros appearing to the right of non-zero digits after the decimal point are significant.

Examples:

  • '26.3400' has six significant figures: 2, 6, 3, 4, 0, and 0 
  • '0.00263400' also has six significant figures (zeros before the '2' are not significant)
  •  '98.00' has 4 significant figures
4.  All zeros appearing in a number without a decimal point and to the right of the last non-zero digit are not significant unless indicated by a bar.  

Examples:
  • '7500' has two significant figures: 7 and 5 as the zeros are not considered significant because they do not have a bar
  •  '7500.0' has five significant figures

It is often necessary to determine from context whether trailing zeros in a number without a decimal point are intended to be significant.

Digits may be important without being 'significant' in this usage. For instance, the zeros in '1300' or '0.005' are not considered significant digits but are still important as placeholders for establishing the number's magnitude.  

A number with all zero digits (e.g. '0.00') has no significant digits, because the uncertainty is larger than the actual measurement.