Accuracy and precision

Accuracy and precision are both terms used to describe how close a measured value is to the true value or the accepted value.

Accuracy is how close a measured value is to the true or accepted value. A measurement can be very accurate but not very precise, or it can be very precise but not very accurate. Imagine shooting an arrow at a target. In this example, accuracy is how close the arrow is to the bullseye (the true value) and precision is how close all the arrows are to each other (even if they’re nowhere near the bullseye). Precision is not the same as accuracy.

Precision is how close all the measured values are to each other. If you shoot an arrow many times, and all the arrows are very close together (but none of them hit the bullseye), then this is an example of a precise shot. The arrows were close to each other, but not very accurate.

In short, accuracy is how close a measured value is to the true or accepted value and precision is how close all the measured values are to each other.