# What is percent error?

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percent error is the deviation from accuracy per 100 units, calculated by the formula,

(obtained reading - accurate value) / (accurate value) * 100 %

e.g if a coin is 2mm thick, but your reading comes out to be 2.2mm, then % error is

(2.2 - 2) / 2 * 100%

= 0.2 / 2*100 %

=10%

if you get a reading of 0.8 mm,

% error = (0.8 - 2.0) / 2 *100%

= -10%

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• Percent Error Definition

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• What Is Percent Error

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• Before getting into percent error, let's define two terms.

Actual or Theoretical answer: This answer comes from working the experiment through equations before you actually run the experiment. It's called "actual" because there will always be an error associated with your observed answer.

Here is a scenario where you would use percent error:

You are running an experiment that is testing the law of gravity. On paper you figure out your "actual answer" and then using a stopwatch, you figure out your "observed answer." You compare both answers using "percent error."

Percent error = (observed - actual) / (actual) * 100

A practical way you would use percent error is to see how closely a machine you've designed behaves in real life with its theoretical design. You usually want percent error to be as low as possible. It means your experiment is right on with the theoretical equations.

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