1. Accuracy and Precision
Much of science has to do with the collection and manipulation of quantitative or numerical data.
The value of computations using numerical data is greatly dependent on the accuracy and precision of that data.

2. Measured Numbers
When you use a measuring tool is used to determine a quantity such
Your height
Volume of a liquid
Time to run a mile
the numbers you obtain are called measured numbers.

3. Exact Numbers Discrete Data Obtained when you count objects
2 soccer balls
60 BB’s
1 watch
4 pizzas
Obtained from a defined relationship
1 foot = 12 inches
1 meters = 100 cm
Not obtained with measuring tools
We will later learn that these numbers do not limit the number of significant figures reported.

4. Liquid Volume

5. Accuracy and Precision
There is always some degree of ERROR in a measurement. This is due to:
Precision of the Equipment
Accuracy of the Measurement

6. ACCURACY Accuracy is how close a number is to what it should be.
determined by comparing a number to a known or accepted value.

7. PRECISION
Precision is how close repeated (successive) measurements are to each other.
It is sometimes defined as reproducibility
Precision is shown by the number of decimal places assigned to the measured number.
The precision of a value determines the number of significant figures.

8. Both Accuracy and Precision depend on the calibration and the quality of the measuring tool.

9. Accuracy and Precision
Accuracy and precision can not be considered independently
A number can be accurate and not precise
A number can be precise and not accurate

10. Example 1: How old are you? I am 16 years old
I am 15 years and 8 months old
I am 15years, 8 months, and 5 days old
I am 15 years, 8 months, 5 days, and 10 hours old

11. Accuracy vs. Precision for Example 1
Each of these statements is more accurate and more precise than the one before it.
Statement two is more accurate and more precise that statement one.
Statement three is more accurate and more precise than statement two.

12. Example 2: How long is a piece of string?
Johnny measures the string at 2.63 cm.
Using the same ruler, Fred measures the string at cm.
Who is most precise?
Who is most accurate?
The actual measurement is 2.65 cm.

13. Accuracy vs. Precision for Example 2
Johnny is fairly accurate and also very precise.
Fred is very precise, however, he is not very accurate. His lack of accuracy is due to using the ruler incorrectly.

14. Example 3 Using a centigram balance, Mary measured a sample at 3 g.
Ashley measured the same sample at 3.00 g.
Who is most precise?
Who is most accurate?
The actual measurement is 3.01 g.

15. Accuracy vs. Precision for Example 3
Mary is reasonably accurate. She was not very precise because the balance was capable of measuring to two decimal places.
Ashley is much more accurate because of the precision of her measurement and closeness of her value to the actual value.

16. ACCURACY/PRECISION
You can tell the precision of a number simply by looking at it. The number of decimal places gives the precision.
Accuracy on the other hand, depends on comparing a number to a known value. Therefore, you cannot simply look at a number and tell if it is accurate

17. In Conclusion
In science we depend upon both the accuracy and precision of the numbers we use.
The need for accuracy and precision varies with the circumstance and other measurements being used.