Chapter 3: Measurement:
Accuracy, Precision, and Error
Objectives
• Distinguish among accuracy, precision,
and error of a measurement
Measurements
• Measurement
– quantity that has both a number and a unit
– fundamental to experimental science so must
be able take and evaluate them
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.
Evaluating measurements
• Accuracy vs. Precision
Evaluating measurements
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.
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.
–.
Evaluating measurements
• To determine Percent Error:
– The percent error is the absolute value of the
error divided by the accepted value, multiplied
by 100%.
–.
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?
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
–.
1.3 C
100.0 C
100%  0.013  100%  1.3%