Grade: Senior
Subject: Science

#577. Precision and Accuracy in Measurements

Science, level: Senior
Posted Wed Aug 19 16:14:20 PDT 1998 by Michael H. Edmondson (
Hardaway High School, Columbus, GA USA
Materials Required: Paper, pencil, calculator
Activity Time: One period
Concepts Taught: Use of precision and acuuracy in science measurements

Precision and Accuracy

Precision refers to the closeness (agreement) of measured values, based upon some accepted standard of "closeness" (generally called a percentage error.)

Examples: 10.2, 10.6, 10.4
Allowing a 15% error (which is, by the way, rather large) these values are precise.

Accuracy refers to the closeness to an accepted value.

Examples: Measured values are 9.6 and 9.7. The accepted value is 9.89. Accuracy is good in this case, as is the precision. They are very close (within an average 0.24 of the accepted value) and closely agree with each other (only 0.1 difference.)

Example: 6.2, 6.4, 6.38 Accepted value: 10.27
Good precision, poor accuracy

Example: 6.3, 9.8, 28.12 Accepted value: 0.023
Horrible accuracy and the precision is even worse!