1. Measurements: Precision, Accuracy and Uncertainty

2. Measurements in General
Always record 1 more decimal place than the smallest division of the instrument by estimation
Because this last digit is only an estimate, it’s said to be uncertain. The ones before that are certain.
All measurements have a degree of uncertainty

3. Measurement of Distance
Top ruler: divided into units of 0.1 (certain) so estimate the 0.01 digit (uncertain)
Bottom ruler is
divided into units
of 1 (certain) so
guess the 0.1 digit
(uncertain)

4. Measurement of Liquids
For most liquids, measure from the bottom of the meniscus

5. Measurement of Liquids
Mercury (Hg) has a convex meniscus (B), for which you would measure from the top
Concave/convex determined by surface tension between the liquid and the container

6. Convex Meniscus of Mercury

7. Precision Precision tells you how close measurements are to each other
More decimals = more precision!
Compare the following 2 sets of data
1, 0, 0, 1, 1
1.0000, , , ,

8. Precision Precision tells you how close measurements are to each other
More decimals = more precision!
Compare the following 2 sets of data
1, 0, 0, 1, 1  Are these close? Hard to tell
1.0000, , , ,  pretty clear

9. Accuracy
Accuracy tells you how close a measurement is to the accepted value
You must know or be able to find the accepted value to know if a measurement is accurate
If accepted value is not known, there’s no way of determining accuracy, even if precision is high

10. Precision & Accuracy