Accuracy and Precision

Accuracy

How close the measured value is to the true value

Precision

how close the measured points are to each other

Precise and accurate

Points of measurement that are close together and close to the true value

Not precise, not accurate

Points of measurement not close to each other and not close to the true value.

Precise, not accurate

I fire five arrows into a target they are all close together but not close to the center of where was aimed

Precise and accurate

I fire five arrows and all five of them land in the direct center of where was aimed.

Accurate, not precise

I fire five arrows at a target. They all land close to the desired area but not close together

Not precise, not accurate

I fire five arrows at a target. they don't land close together or close to the desired area

Low Precision, Low accuracy

not repeating, not in the same place

High Precision, low accuracy

Has repeated the darts in the same place, but is not hitting the bullseye

High accuracy, low precision

All are close to the bullseye, but not all in the same place

High accuracy and high precision

Darts are clustered in the same place, and are clustered in the bullseye

Accuracy

How close to a correct answer a measurement is to a true or known value

Precision

The degree to which repeated measurements show the same result.

Callibration

How close a measuring tools markings are to a known, and correct, value