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Percent Error (deviation) is a measure of the accuracy of any measured value.  It is easily determined by comparing the difference between the actual value and the measured value to the actual value itself.   Percent Error is expressed mathematically as:

In mathematical terms, percent error is simply an expression of the amount of deviation from the accepted value, expressed as a percent.   Percent error can be determined easily if you have a known value and an accepted value for your measurements.  In the absence of an accepted value, you may conduct several trials for each measurement and use your average of those trials as your accepted value.

Example:
The mass of a rock was measured by a student and determined to be 325 grams.  The mass of the rock was then measured by the entire class.  The class average value was 320 grams.  Calculate the percent error in the forst student's measurement of the rock's mass.

Error = 1.56 %

Practice Problems:

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Copyright 1997-2007, Michael Liener