Flow measurement accuracy refers to the accuracy of the flow measurement system, it is the accuracy of the flowmeter itself is different. Only the flowmeter itself, good performance, high accuracy, not necessarily to obtain a higher measurement accuracy. To ensure the accuracy of the flow measurement system, in addition to a reasonable selection, proper installation and commissioning, timely maintenance and maintenance, the application of intelligent technology to measure some of the errors may be just right compensation and correction is also an effective method. For example, the liquid temperature coefficient of expansion compensation, the gas temperature, pressure and compression coefficient to compensate for the differential pressure flowmeter Reynolds number and flow coefficient of expansion to compensate for a variety of flowmeter flow coefficient of non-linear Compensation, volumetric flowmeter, vortex flowmeter to compensate for the impact of the temperature on the ultrasonic flowmeter velocity distribution compensation. This compensation and correction is a systematic approach to the detection part of the inherent, relying on its own can not be overcome to deal with the error, so eliminate or be basically eliminated. Practice shows that this method is simple and effective, very promising. In order to ensure the accuracy of many methods of measurement, online real-flow calibration plays an important role. Previously, most of the off-line method of calibrating flowmeter, the use of the method of flowmeter calibration error correction, although the higher accuracy, but because of its reference line when the reference conditions and the actual use of different nature of the test fluid and the actual use Of the fluid is different from the test when the environmental conditions and the use of the instrument is not the same as the actual environment, resulting in additional use of errors, reducing the measurement accuracy. On-line real-time calibration is an effective method to solve this problem. For example, the oil metering station in the construction phase to set aside the standard volume pipe connection, access to the standard volume tube, the valve can be achieved through the switch to the metering station flow meter on-line real-time calibration. Now, in the natural gas distribution station also requires the use of online real-flow calibration method.