Accuracy vs. Precision

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Accuracy vs. Precision
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Accuracy

• Refers to the closeness of measurements to the
  correct value.

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precision

• Refers to the closeness of a set of measurements
  of the same quantity made in the same way.
  Therefore, measured values that are precise are
  close to one another, but not necessarily close
  to the accepted value.

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Significant Figures

• Consist of all the digits known with certainty
  plus one final digit, which is somewhat uncertain
  or is estimated.

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EXAMPLE

• If you measure the length of a nail with a ruler
  and found it to be less than halfway between 3.6
  and 3.7 cm longwould it be 3.61, 3.62, 3.63, or
  3.64 cm long?

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• The third digit in the length must be estimated.
  This estimated digit tells anyone reading the
  measurement that the nail is longer that 3.6 cm.

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Presentpacific Absentatlantic
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• 0.4321
• Presentpacific
• 29040
• Absentatlantic
• 0.693020
• 200005

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How many significant figures are in each of the
following?

• 1. 290000000
• 2. 0.000314
• 3. 0.189900000
• 4. 500000

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Exact numbersno sig. fig.

• 7 days 1 week
• 25.00 have exactly 25 dollars
• 12 inches in 1 foot
• 60 minutes in 1 hour
• 100 cm in 1 meter

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error

• exp.-accepted
• error accepted x 100