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1. Chapter 3: Measurement:
Accuracy, Precision, and Error

2. Objectives
• Distinguish among accuracy, precision,
and error of a measurement

3. Measurements
• Measurement
– quantity that has both a number and a unit
– fundamental to experimental science so must
be able take and evaluate them

4. Evaluating measurements
• Accuracy
– measure of how close a measurement comes to
the actual or true value of whatever is
measured.
• Precision
– measure of how close a series of
measurements are to one another.

5. Evaluating measurements
• Accuracy vs. Precision

6. Evaluating measurements

7. Evaluating measurements
• Often, we are experimentally determining a
value in the lab that is already known.
– When we do this, we must calculate error in
order to see how accurate and precise our
results are
• In lab reports, you will be required to
determine your error and percent error.

8. Evaluating measurements
• To determine Error:
– The accepted value is the correct value based
on reliable references.
– The experimental value is the value measured
in the lab.
– The difference between the experimental value
and the accepted value is called the error.
–.

9. Evaluating measurements
• To determine Percent Error:
– The percent error is the absolute value of the
error divided by the accepted value, multiplied
by 100%.
– .

10. Practice: error and percent error
Question 1
• The accepted value for the boiling point of
water is 100.0°C. In the lab, you
experimentally determined it to be 98.7°C.
What is the error and percent error?

11. Practice: error and percent error
Answer 1
• Given
– Accepted value = 100.0°C
– Experimental value = 98.7°C
• Work
– .
– Error = 98.7°C - 100.0°C = -1.3°C
– .