1. Measuring September 2007

2. Accuracy and Precision Accuracy indicates how close a measurement is to the accepted value. For example, we'd expect a balance to read 100 grams if we placed a standard 100 g weight on the balance. If it does not, then the balance is inaccurate

4. Precision indicates how close together or how repeatable the results are. A precise measuring instrument will give very nearly the same result each time it is used. The precision of a measurement tool is the smallest unit that can be measured with confidence. It depends on the fineness of the scale on the tool.

5. The thermometers found in high school labs are often more precise than they are accurate. It is quite easy to read a thermometer to the nearest 0.2 o C. However the overall calibration can often be off by a degree or more. The temperature shown on the thermometer on the next slide can be read to 34 o C. However, if the thermometer is not of high quality, it would be easy for the real temperature to be off by as much as a degree or more. In other words, the temperature could really be as high as 35 or as low as 33 o C, although the thermometer reads 34.0.

7. Accurate or Precise?? This is a randomlike pattern, neither precise nor accurate. The darts are not clustered together and are not near the bull's eye.

8. Accurate or Precise? This is a precise pattern, but not accurate. The darts are clustered together but did not hit the intended mark.

9. Accurate or Precise? This is an accurate pattern, but not precise. The darts are not clustered, but their 'average' position is the center of the bull's eye.

10. Accurate or Precise? This pattern is both precise and accurate. The darts are tightly clustered and their average position is the center of the bull's eye.

11. Summary A measurement is accurate if it correctly reflects the actual size/value of the object. Precise means exact and refers to the fineness of the measuring tool We can never make a perfect measurement. The best we can do is to come as close as possible within the limitations of the measuring instruments

12. Homework #9 page 10