Accuracy and Precision?

Question

My Physics teacher asked us today what the difference between Accuracy and Precision is, no one knew. He left us hanging. And now I am wondering what the difference between the 2 are?

Answer 1

As Rob said Accuracy is how close your measurement is to the true value.



Precision, in terms of measurement, is how small the units of measurement used are.

For instance, if my speedometer needle is on the fifty mark and I say I'm going 50.000mph I've given my speed with a (bogus) precision of +/-.0005 mph. In reality I could be going about 52 mph, so the accuracy of my measurement is only +/-2mph.



Accuracy, in terms of action, is how close to the desired result the action is.

Precision, in terms of action, is how repeatable the action is.

For instance the size of a group of shots on a rifle target is the precision of the shots. The distance from the bulls-eye of the group is the accuracy.

Answer 2

A measurement is said to be accurate when the measured value is equal to the 'true' value.



However, it's possible to make a series of very precise measurements that are totally inaccurate.



Precision is how close your measurements are together.



For example,

If you used an old metre rule made of wood and then wrote down some measurements of the length of some object: 700mm, 699 mm, 701mm and 699mm; then your results show a high precision because that are all very close to one another. However, If I were then to tell you that this wood metre ruler had shrunk over the years and when compared with a standard modern metal rule it was in fact only 97cm in length, then you can see the the readings while precise are inaccurate due to this systematic error.

Answer 3

Accuracy is how close your results/answers are to the true answer, while Precision increases with using smaller measuring units. Greater accuracy may be attained from being more precise with your measurements.