In a perfect world, all gaging results are spot on. They are both accurate and precise no matter the conditions or by whom or where the gage is used. Unfortunately, this is not the case. These two gage characteristics are both very important. However, we could ask ourselves which one is more important. Perhaps an argument can be made for one over the other.
According to Wikipedia, “In the fields of science and engineering, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity’s true value.” The precision of a measurement system—also called reproducibility or repeatability—is the degree to which repeated measurements under unchanged conditions show the same results.
A measurement system can be accurate but not precise, precise but not accurate, neither, or both. Of course, there are degrees of accuracy and precision, and some errors are always going to exist. However, sometimes—like getting a haircut and putting on a nice suit for a job interview—repeatability can compensate for a certain degree of inaccuracy.
In the metrology business, we frequently get customer requests for gaging applications that are way out of the ordinary. Either the requirement goes against the laws of physics or it pushes conventional gaging beyond its normal limits. Sometimes, the laws cannot be broken and the gage simply cannot be built. In other cases, by understanding accuracy and precision, there is a chance to move the mountain.
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