Accuracy and precision are two ways to measure results. Accuracy measures how close the results are to the true or known value. Precision, on the other hand, measures how close the results are to each other. Both measurements are useful for tracking and reporting on the results of a project.
Normally, the terms accuracy and precision are used interchangeably, but when we talk about measurements, their definition is different. Just because a measurement is exact does not mean it is also precise, and vice versa. Both accuracy and precision are essential aspects of world-class production work.
Although both terms are commonly used as synonyms, within metrology they are concepts with different and well-defined meanings since when making a measurement it may be precise, but at the same time inexact.
Both accuracy and precision are forms of measurement that define how close you are to meeting a goal or objective. Accuracy measures how close you are to an actual measurement value, while precision shows how close the measured values are to each other. In short, accuracy is the degree of difference between the measured value and the real value and precision indicates the dispersion between the data obtained.
The precision is defined as: The degree of coincidence between the independent results of a measurement, obtained under stipulated conditions.
The accuracy is defined as: The degree of agreement between the result of a measurement and a true value of the measurand.
As mentioned, accuracy is the difference between the measured value and the true value. Therefore, an exact measurement will be one that has the smallest possible error in the measurement.
Accuracy can be determined by making a single measurement unlike precision and does not have an associated numerical value.
Precision measures the repeatability of the measurement or the dispersion of the data among themselves and can be evaluated by statistical parameters such as the standard deviation, the variance or the coefficient of variation. Unlike accuracy, several measurements will be necessary to evaluate precision.
- Accuracy indicates the quality of the result.
- Precision indicates the agreement between measurements.
A measuring device can be very precise, if it always gives the same or very similar result. However, it does not have to be exact if the result is not similar to the real value. In fact, good measuring instruments must be exact and precise simultaneously.
The class is the way to specify the accuracy of a measuring instrument.
The class is specified in ASME B40.100 (accuracy classes 0.1 to 5% of scale range) and EN 837 (accuracy classes 0.1 to 4% of scale range). The accuracy class specification is usually expressed as % of the scale range, but is designated according to these standards, for example, a pressure gauge whose accuracy is 0.5% of the scale range, means that according to ASME B40.100, it is Grade 2A.