1. Precision, Accuracy and Error

2. Precision When measuring, most of the time our measurements are estimates. How precise are these estimates? Precision is the ability of a measurement to be consistently reproduced. Precision depends on the measuring tool used. The smaller the unit of measure the more precise the measurement.

3. Examples: Which is more precise? 8 cm or 82 mm 3 ft or 37 in.

4. Precision Unit The precision unit of an instrument is the smallest unit on it. What is the precision unit for the length of a football field? Would it be more precise if meters were used?

5. Greatest Possible Error The Greatest Possible Error is ½ of the smallest unit of measure or the precision unit. For example: A plank measures 30 in. The smallest unit of measure is one inch. So the GPE is ½ inch. So the actual measurement is in the range of 30 + ½ inches

6. Find the GPE 56 ft 41.5 km 32.4 m 36 ½ in.

7. Examples A pencil is measured to be 19mm long. What is the interval of the actual length? Find the interval of length for a book measured to be 12 inches long.

8. Accuracy Accuracy refers to how close a measurement is to the actual value. A measurement can be precise (you measured the same way 3 times in a row) but not accurate (you measured it wrong 3 times in a row)

9. Significant digits The accuracy of a measurement is sometimes shown by significant digits MeasurementUnitSignificant Digits # Significant Digits 120.1m.1m1,2,0,14 120m1m1,2,03 1.2m.1m1,22 0.048cm.001cm4,82 3.06cm.01cm3,0,63

10. Which is more accurate? The measurement with the most significant digits. 26 cm or 26.0 cm 558.34m or 558.3 m.00512mm or.0051mm

11. Absolute and Percent Error Absolute error E a =|estimated measure – actual measure| Percent error =