2. Measuring instruments refer to devices, instruments, measuring tools and reference materials that can directly or indirectly measure the value of the measured object. Measuring instruments are widely used in production, scientific research and people's lives and play a very important role in the whole measurement legislation. Because the unification of national values is first reflected in the accuracy and consistency of measuring instruments, which are not only the main object of supervision and management, but also the technical basis for the measurement department to provide measurement guarantee.