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Measurement accuracy and the accuracy of measuring instruments. Seven international organizations, namely the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), the International Organization of Legal Metrology (OIML), the Bureau International des Poids et Mesures (BIPM), the International Union of Pure and Applied Physics (IUPAP), the International Union of Pure and Applied Chemistry (IUPAC), and the International Federation of Clinical Chemistry (IFCC), revised the \"International Vocabulary of Basic and General Terms in Metrology\" in 1993 (hereinafter referred to as \"VIM\"). In September 1998, China’s **Quality and Technical Supervision Bureau issued the JJF1001‑1998 standard titled \"General Terms and Definitions in Metrology\" (hereinafter referred to as \"JJF\"), which is a metrological technical specification. In the above two texts, there are clear definitions and explanations regarding measurement accuracy, the accuracy of flow meters, and accuracy grades. Based on these documents, this article outlines the issues that must be taken into account when using these concepts. 1. Accuracy is translated as accuracy (this term can be used to describe measurement results as well as the readings given by measuring instruments). When used for measurement results, it indicates the degree of agreement between the measurement result and the true value of the quantity being measured. When used in measuring instruments, it is defined as the ability of the instrument to give values close to the true value; in all such cases, accuracy is a qualitative concept rather than a quantitative one. Therefore, accuracy is not like measurement error or measurement uncertainty; it is not a physical quantity and does not have a quantitative value. Measurement error is defined as the difference between the measurement result and the true value of the quantity being measured; it is the difference between these two values and can be expressed quantitatively. Accuracy, however, cannot. Quantification refers to expressing it in numerical values. For example, when we say that the indication error of a certain measuring instrument is –7.8 mA, this is a quantitative expression that gives the value, namely –7.8 mA. But we must never say that the accuracy of this measuring instrument is –7.8mA or ±7.8mA, or less than or equal to 7.8mA. When the fiducial error of a measuring instrument is not greater than 0.01 (1%), its accuracy is generally considered to be grade 1 in accordance with the standards or calibration procedures applicable to that instrument. But it is an accuracy of level 1, not an accuracy of 1%. Note: 1% is a numerical value. 2. Accuracy Class In the VIM and JJF standards, the accuracy class refers to the category or grade of a measuring instrument that meets certain metrological requirements, ensuring that its errors remain within specified limits. In metrology, order and class are two distinct concepts. It is clearly specified in the metrological technical specification JJG1027‑91 \"Measurement Errors and Data Processing\". Grade is a category divided according to the magnitude of measurement uncertainty. A grade is a category determined by the magnitude of the indication error of a measuring instrument (for the definitions of uncertainty and indication error, including the definition of the indication error of instruments, please refer to JJF). For example: gauge blocks are classified both by grade and by class, standard batteries are also classified both by grade and by class, whereas standard piston pressure gauges are only classified by grade without any classes. The grade of some instruments is determined based on the reference error (a type of relative maximum allowable error). When we say that a measuring instrument belongs to a certain grade or class, it is a qualitative assessment of the instrument’s accuracy. 3. The quantitative issue of accuracy: It is incorrect to equate accuracy with measurement error, limit error, or uncertainty, although all of these terms refer to the ability to approach the true value. Quantities that can be used for quantitative description include: measurement error, relative error, standard uncertainty u, expanded uncertainty U, and U ； For measuring instruments, there are values such as the indication error p, the maximum allowable error, and the reference error. When these quantities are given, a numerical value can be provided without exception. We can consider accuracy to be just a general term for them. If we say the accuracy is 7.8mA, then is this 7.8mA the error? Is it the expanded uncertainty including the factor k=2? Is it still the expanded uncertainty for k=3? It is not clear whether it is the maximum allowable error or the limit error, etc. Therefore, if we are to quantitatively determine the ability of a measuring instrument to approach the true value, we must specify what kind of quantity the given value represents, rather than simply referring to it as accuracy. The current misuse of the term \"accuracy\" is quite common, and it deserves proper attention. Especially in contract negotiations, accuracy is a term that cannot be quantified; it cannot be used as a basis for acceptance, which can lead to unnecessary losses.