Accuracy tells us how close

a particular measurement is to the correct value.

For instance,

how close is the reading of a thermometer to the actual temperature?

Precision is the consistency of repeated measurement.

In other words, are the results consistent

each time something is measured?

The more consistent the results,

the more precise the measurement.

It is possible to have a precise measurement that is not accurate.

It is also possible to have an accurate measurement that is not precise.

The best measurements are both accurate and precise!

Let us look more closely at the difference between accuracy and

precision using an archer and target.

The archer is accurate when he hits the bull's eye.

He is precise when he can consistently hit the same spot on the target,

in this case the bull's eye, over and over again.

This archer is both accurate (he hits the bull's eye) and

precise (he is able to hit the same area of the bull's eye repeatedly).

It is also possible for the archer to be precise, but inaccurate.

If he misses the bull's eye, he is inaccurate; he has missed the mark.

But if he can consistently and

repeatedly hit the target in the same place,

even if it is not the bull's eye, he is precise.

On the other hand, the archer may be accurate, but not precise.

If he strikes the bull's eye or right next to the bull's eye,

but his arrows are not consistently placed,

then the archer is accurate, but not precise.

In this case,

the arrows would be spread across the bull's eye

rather than clumped together in a small area.

If our archer is having a really bad day,

he might even be inaccurate and imprecise.

In this case,

his arrows will strike the target in a random pattern and

he will not hit the same part of the target time after time.