Precision, Accuracy, and Error
West Baton Rouge Parish Schools
Grade 6 GLE 31
Precision in Measurement
Precision is how close the
measured values are
to each other.
Accuracy in Measurement
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
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
High Accuracy… Low Precision
High Precision … Low Accuracy
If we measure the length of a foot-ruler and get
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
These measurements are precise but necessarily
The foot-ruler may actually be metric ruler of 30.0
cm long. Our measurement is precise but not