ACCURACY AND PRECISION: UNDERSTANDING THE DIFFERENCE

Precision, accuracy and resolution are all terms that we encounter frequently in daily life and certainly in the specification of testing equipment. The illustration above shows the interrelationships between these terms.

Accuracy is precision with calibration. This means that you not only repeat time and again, but also hit what you are aiming for within prescribed error limits.

Precision means that you can hit the same point time and again within certain limits. But as the target illustrates, you can be precise without “hitting the bull’s-eye.”

Accuracy, precision and calibration are similar terms but with very dissimilar meanings.

Accuracy is difficult without good precision. Precision, however, does not ensure accuracy. Precision with calibration results in accuracy.

Resolution is the ability of a system to detect small changes but does NOT mean that the value of the changes is accurately reported. When you look at the specification of measurement devices, remember that the only meaningful measure is accuracy.

However, it is also possible to be misled by an accuracy specification. What really matters is the system accuracy. For example, a load cell may have a particular accuracy specification, but that does not mean that you will get that accuracy once you have connected it to your test system. The overall system accuracy is also affected by the load cell conditioning electronics and the readout resolution.

Instron® prides itself on specifying system accuracies very precisely and unambiguously so that you do not doubt what accuracy you will achieve. This includes a clear statement of the range over which the accuracy holds for particular systems.