Incorrect placement of the workpiece will result in inaccurate measurement accuracy of the gas gauge. At present, the measurement degree of the gas meter itself is still very high, and it can be measured for multiple parts, such as the inner diameter and roundness of the small hole, etc., can be used for measurement, and the measurement does not need to contact, there is no mechanical friction, so there is no measurement error in the return trip. However, the reason for the uncertainty is that the air momentum meter is for some small pipes to complete the measurement, once the position is not correct, it will affect the measurement data.