User:

Accuracy and precision

The terms accuracy and precision have different meanings in the context of measurement.

Accuracy is the difference between your reported measurement and the true (but unknown) measurement. It is generally imposible to calculate the accuracy of a measurement, because it requires us to know the true measurement.

Precision refers to the perceived level of accuracy of a measuring tool.We generally assume a measurement tool, such as a ruler, with a greater degree of precision (that is, smaller units or more closely spaced marked) results in measurement with a greater degree of exactness (because we perceive there will be less rounding error).

Jenny and Marco measure the height of a chair. Jenny records the measurement as 3.4 feet, and Marco records the measurement as 3.42 feet.
a. Which measurement is more precise?
b. Which measurement is more accurate?

 a. The measurement 3.42 is more precise. b. Without further information, it is impossible to determine which measurement is more accurate in this situation. However, we expect 3.42 feet to be more accurate tahn 3.4 feet, because it may involve less rounding error.