Significant figures include all certain digits plus one and only one uncertain digit.

Significant figures relate to measurements...they may only have one digit of uncertainty (estimated number).

The digits 1, 2, 3, 4, 5, 6, 7, 8, and 9 are always significant.

Zeros are not significant at the end of a whole number which does not have a decimal point. 

   Examples:  3400 (2 significant  figures)    2000 (2 sig fig)

Zeros are not significant at the beginning of a deci-number which does not have a whole number.

   Examples:  0.0034 (2 sig fig)    0.0002 (1 sig fig)

All other zeros are significant.

   Examples:  3400.  (4 sig fig)    200.0 (4 sig fig)    1.0034 (5 sig fig)    2.00020 (6 sig fig)

Definitions contain an unlimited number of significant figures. 

   Examples:  double the answer and p (contain an unlimited number of decimal places)

Special case - when some zeros are significant and some are not, use a line to  show which ones are.

   Examples:  3400 (3 sig fig)    2000 (3 sig fig)

Additional Information

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