The selection of measuring instruments should be based on technology and economy, so that the selection of their types and specifications can adapt to the characteristics of workpiece shape, position, size and measuring parameters, as well as measuring characteristics (such as maximum permissible error, stability, measuring range, sensitivity, resolution, etc.). ) can properly meet the predetermined requirements, should be enough but not too high, should be considered at the same time with the choice of measurement methods. 1, according to the workpiece processing batch: ordinary measuring tools are selected for small batch; A large number of gauges and gauges are selected to improve the measurement efficiency. 2. According to the structure and weight of the workpiece: the light and simple workpiece can be measured on the measuring tool, and the heavy and complex workpiece should be measured with the upper measuring tool, that is, the measuring tool should be taken to the workpiece. 3, according to the size of the workpiece size and requirements to determine the specifications of measuring instruments. In order to make the measuring range of the measuring instrument can accommodate the workpiece, the probe can extend into the measured part. 4. Select the measuring instrument according to the error (tolerance) required by the workpiece. In general, the maximum permissible error of measuring instruments is1/3 ~110 of the workpiece tolerance. If the measured workpiece belongs to measuring equipment, its tolerance must be110; If the workpiece to be tested is a general product, its tolerance is1/3 ~1/5; If the conditions of the measuring instrument are not allowed, it can also be 1/2 of its tolerance, but the confidence level of the measurement results will be reduced accordingly. 5. When choosing the sensitivity, we should pay attention to the fact that the sensitivity of measuring instruments is too low, which will affect the measurement accuracy, and it is difficult to reach the equilibrium state in time if the sensitivity is too high. The measurement of measuring instruments should follow the maintenance, overhaul and appraisal plan of measuring instruments to ensure the accuracy, sensitivity and precision of the measuring instruments used. To use the measuring instrument correctly, please refer to the instruction manual or relevant reference materials, and keep it clean, rust-proof and shockproof (some need antimagnetic and compressive resistance, etc.). ), and properly stored.