Uncertainty is the component of a declared value that characterizes the range within which a real value is affirmed. An estimate of uncertainty should correct errors in all possible effects (systematic and random) and is therefore generally the most appropriate way to express the accuracy of the results. This is in accordance with ISO guidelines. However, in many measurement situations, the systematic error is not corrected and only an accidental error is taken into account in the measure of uncertainty. If only accidental errors are included in the uncertainty estimate, this is a reflection on the accuracy of the measurement. Accuracy is the proximity of a measure to fair value for this measurement. The accuracy of a measurement system refers to the proximity of the concordance between repeated measurements (repeated under the same conditions). Measurements can be both accurate and precise, accurate, but not precise, accurate, but not accurate, but not accurate or not. The correct use of terms such as measurement error, accuracy, veracity, accuracy, measurement uncertainty and other expressions is essential for a professional approach to analytical measurement. This article is the first in a two-part series on analytical terminology.

It explains what these terms mean in a laboratory environment and how you can build confidence in the quality of your own measurement results. In the fields of science and technology, the accuracy of a measurement system is the degree of proximity of measurements from a quantity to the actual value of that quantity. [2] The accuracy of a measurement system that relates to reproducibility and repeatability is the degree to which repeated measurements under unchanged conditions show the same results. [2] [3] Although the two words are commonly synonymous with precision and precision, they are deliberately contrasted in the context of the scientific method. The results of measurements taken under identical conditions are never error-free, but scattered around an average (B). Depending on the quality of the measurement method, the average deviates more or less from a generally accepted reference value considered to be the real value (A) (Figure 1).