1. Accuracy and Precision
Measurements are qualitative or quantitative.
Qualitative measurements give results that are descriptive and non-numerical.
Example:
Quantitative measurements give results that are definite, usually as numbers and units.

2. Accuracy and Precision
Measurements work best when they are accurate and precise
Accuracy is a measure of how close a measurement comes to the actual or true value of whatever is measured.
To evaluate the accuracy of a measurement, it must be compared to the correct value.
Precision is a measure of how close a series of measurements are to one another.
The precision of a measurement depends on more than one measurement.

3. Accuracy and Precision

4. Accuracy and Precision

5. Accuracy and Precision
In this picture, all of the darts land on the bulls-eye which illustrates good precision and accuracy.
In this picture, all of the darts land near each other, but away from the bulls-eye which illustrates good precision, but poor accuracy.

6. Accuracy and Precision
Here the darts are not close to each other, but are close to the bulls-eye indicating poor precision, but good accuracy.
Finally, the darts are not close to each other or near the bulls-eye indicating both poor accuracy and poor precision.

7. Accuracy and Precision
Sometimes there is a difference between the accepted value and the experimental value.
This difference is known as error.
Error = accepted value – experimental value
Error can be positive or negative depending on whether the experimental value is greater than or less than the accepted value.

8. Accuracy and Precision
Often it is useful to calculate relative error, or percent error.
Percent error = error x 100%
accepted value
The percent error will always be a positive value.