Strengthening metrological supervision and management is of great significance for promoting social and economic development. Metrology, as an important means to enhance metrological supervision and management, requires starting from two aspects: quantity value transmission and quantity value traceability to ensure the consistency and validity of measurement results. Quantity value transmission and quantity value traceability are important means to guarantee metrological accuracy and consistency. They are interrelated and involve reciprocal processes. In daily life, it is necessary to grasp the different characteristics and properties of measuring instruments and strengthen the work of quantity value transmission and quantity value traceability. ### What Does Quantity Value Traceability Mean? The consistency of quantity value traceability is a prerequisite for mutual recognition of measurement results. Only by attaching great importance to the traceability of quantity values in laboratories and ensuring that all test results can be traced to national or international measurement standards can the fairness, consistency, accuracy, and legal validity of test results provided by laboratories be guaranteed. The main ways for laboratories to achieve quantity value traceability include: equipment calibration or verification, use of certified reference materials, participation in proficiency testing or inter-laboratory comparisons, etc. As the ISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories and the Laboratory Qualification Accreditation Review Criteria have been implemented for many years, various testing institutions now attach great importance to quantity value traceability. Testing equipment is sent to qualified metrological institutions for verification or calibration, or internal calibration is adopted, and the management of certified reference materials is relatively standardized. ### Scope of Quantity Value Traceability For laboratories, quantity value traceability is generally required for the following objects: 1. **Instruments and equipment**: Mainly refer to instruments and equipment and related parameters that will affect the test and/or calibration results. 2. **Reference standards**: A reference standard is a measurement standard that usually has the highest metrological characteristics in a given region or organization. It is the highest metrological standard of a laboratory with quantity value functions and should be verified by a legal metrological technical institution. 3. **Reference materials (reference substances)**: A material or substance that has one or more sufficiently homogeneous and well-defined characteristics, used to calibrate measuring devices, evaluate measurement methods, or assign values to materials. A reference material that is traceable and accompanied by a certificate is called a certified reference material. Laboratories should use certified reference materials as much as possible. If no certified reference material is available, the laboratory should prove the accuracy and traceability of the quantity value through comparison tests, proficiency testing, etc. ### Precautions for Quantity Value Traceability of Instruments and Equipment 1. When verifying instruments and equipment, all metrological parameters should generally be inspected; when calibrating or testing instruments and equipment, all or part of the metrological parameters can be selectively inspected according to the needs of specific test work to avoid unnecessary waste. 2. After obtaining the calibration (test) certificate for instruments and equipment, it is necessary to confirm the compliance of the calibration (test) results with the requirements of the test work. If necessary, correction factors should be considered and confirmation records should be formed. For instruments and equipment with specified technical conditions or standards, compare the calibration (test) results with the technical conditions or standards to determine whether the instruments and equipment can be used; for instruments and equipment without specified technical conditions or standards, the (expanded) measurement uncertainty can be calculated according to the measured object and measurement method, and then compared with the technical requirements of the measured value. It should not exceed 1/3 of the maximum allowable deviation (error) of the measured value to determine whether the instruments and equipment can be used or used with restrictions. 3. Professional laboratories should select units with corresponding qualifications when sending instruments and equipment (reference standards and reference materials) to external verification/calibration institutions. 4. Instruments that are temporarily sealed and not in use should go through suspension procedures, be filed in the instrument files, and be labeled as out of service to avoid misuse. Out-of-service instruments and equipment may not be included in the verification/calibration plan. Once they need to be reused, they should be verified/calibrated or checked to meet the requirements before being put into use. ### Important Methods for Quantity Value Traceability of Instruments and Equipment Verification and calibration are important methods for quantity value traceability of instruments and equipment. Verification is an activity to find out and confirm whether a measuring instrument meets legal requirements. Calibration is a set of operations to determine the relationship between the quantity value provided by a measurement standard and the corresponding indication under specified conditions. The two have similarities but also obvious differences. Verification is a comprehensive evaluation of measuring devices that require mandatory verification by qualified metrological departments or legally authorized units in accordance with metrological verification regulations. It is a top-down quantity value transmission process, which determines whether the measuring device is qualified or unqualified, and provides the accuracy level or maximum allowable error that the measuring instrument meets. Generally, it does not provide the uncertainty of measurement results. Calibration is a set of operations for institutions to adopt self-calibration, external calibration, or a combination of self-calibration and external calibration. It evaluates the indication error of measuring devices other than mandatory verification in accordance with national metrological calibration specifications, or relevant parts of metrological verification regulations for non-mandatory verification measuring instruments. It belongs to a bottom-up quantity value traceability process. Generally, it does not require a determination of qualification or unqualification, but needs to provide measurement uncertainty. Testing institutions need to formulate relevant work plans or schemes before carrying out quantity value traceability work for instruments and equipment, and determine the relevant information of the instruments and equipment to be verified and calibrated and the commonly used verification and calibration points. The biggest difficulty in confirming the calibration results of instruments and equipment is the lack of judgment standards and basis for calibration results. Commonly used verification and calibration points are determined according to daily testing needs and relevant testing standard methods. For example, according to the *National Food Safety Standard - Determination of Moisture in Food* (GB 5009.3—2016) using the direct drying method to determine grain moisture, the working temperature of the drying oven is 101–105°C, so the calibration temperature of the drying oven can be set to 103°C, and the calibration temperature of the mercury thermometer monitoring the drying oven temperature can also be set to 103°C. The calibration temperature of the muffle furnace can be set according to the ash determination temperature of powder samples and the reagent drying temperature, and the water bath can be set with reference to the constant temperature requirements for sample testing. Bottle-top dispensers are often used to absorb digestion solutions in the pretreatment process of metal element digestion in grain samples. The maximum range of bottle-top dispensers is about 50 mL, but when calibrated in accordance with *Pipettes* (JJG 646—2006), the maximum calibration range provided in the regulation is 10,000 μL, which cannot cover the range of bottle-top dispensers, resulting in the problem that calibration results cannot be evaluated. In daily work, the use of bottle-top dispensers can be fixed, and the frequently used pipetting range points can be selected for calibration to facilitate the evaluation of quantity value traceability results. **Summary**: The consistency of quantity value traceability is the basis for the credibility of measurement results and the guarantee for the accuracy and reliability of test data. Doing a good job in quantity value traceability is the basis and necessary condition for testing institutions to carry out quality activities. All testing institutions should attach great importance to the quantity value traceability work of instruments and equipment, carry out the quantity value traceability of instruments and equipment in a standardized and orderly manner, prevent the distortion of test results caused by deviations in instrument performance, give full play to the technical service role of testing institutions, so as to effectively ensure the accuracy and comparability of test results and the scientificity and fairness of test conclusions. Sources: *Building Materials and Decoration*, *Food Safety Guide*, *Quality and Testing*