Measurement Precision, Accuracy, and Error

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					        Measurement:
Precision, Accuracy, and Error

  West Baton Rouge Parish Schools
          Grade 6 GLE 31
Precision in Measurement
         Precision
Precision is how close the
  measured values are
      to each other.
 Accuracy in Measurement

                Accuracy
Accuracy is how close a measured value is
       to the actual (true) value.
      Degree of Accuracy
  Accuracy depends on the instrument you are measuring with.
  But as a general rule:

  The degree of accuracy is half a unit each side of the unit of
  measure




  If your instrument                            If your instrument
measures in "1"s then                           measures in "2"s
any value between 6½                              then any value
       and 7½ is                               between 7 and 9 is
  measured as "7"                               measured as "8"
Error in Measurement
encompasses both the imprecision of data and its
                inaccuracies
High Accuracy… Low Precision
High Precision … Low Accuracy
If we measure the length of a foot-ruler and get
values of

12.01 in, 12.00 in, 11.99 in, 12.00 in.

These numbers are precise enough for us to
believe that if we measure it again we would get
12.00+0.01 in.
These measurements are precise but necessarily
accurate.
The foot-ruler may actually be metric ruler of 30.0
cm long. Our measurement is precise but not
accurate.