Name: _________________________________Date: _________________________Period: _____
Unit 1: The Nature of Science
Percent Deviation Notes
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Background:
No matter how hard you try, there will always be some error in the measurements you make. This
unavoidable error is the result of your measuring device or the environment in which you are
making your measurements. When communicating the results of an experiment, it is helpful to
communicate the accuracy of your measurements so that the reader understands how much error is
associated with the data you collected.
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If you know the actual value of the object you are measuring, then you can compare your measured
value by finding out how much your value deviates from the actual value. This quantity is often
expressed as a percent and therefore is known as percent deviation or percent error.
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What is the formula for calculating percent deviation/error?
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Percent Deviation =
∣Actual Value - Measured Value∣
Actual Value
x 100
Example 1:
You are asked to calculate the density of a rock and you get an answer of 2.7 g/mL. The actual
density turns out to be 2.3 g/mL. What is the percent deviation?
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Measured Value: 2.7 g/ml
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Actual Value: 2.3 g/ml
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Example 2:
A man named Eratosthenes used 2 wells, the sun, and a camel to calculate the circumference of the
Earth. When converted to modern day units, Eratosthenes found the circumference to be 46,620 km.
Modern satellites tell us that the actual circumference is 40,008 km. How well did Eratosthenes do?
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Measured Value:
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Actual Value: