Precision, Accuracy and Error. Precision When measuring, most of the time our measurements are estimates. How precise are these estimates? Precision is.

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Presentation transcript:

Precision, Accuracy and Error

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.

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

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?

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

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

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.

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)

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, cm.001cm4, cm.01cm3,0,63

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

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