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According to the gas equation of state, the volume of gas at a certain time is related to the current temperature and pressure. Therefore, the calibrated K-factor of gas flowmeter will be affected by the temperature and pressure during the calibration process. Normally, in the ordinary pressure calibration process, the temperature change of calibration medium does not exceed 0.2 degrees, and the influence on the measurement results is about 0.08%. However, the influence on the measurement results can reach 3%~4% due to the different position of the pressure-sampling. An array experiments were carried out on the gas vortex flowmeter (which was most influenced by the pressure-sampling position). It was found that different pressure-sampling positions affect the calibrated K-factor of the gas vortex flowmeters without temperature and pressure compensation, and the degree of influence is proportional to the pressure drop generated by the gas passing through the flowmeter. And the influence is nonlinear. The greater the gas flow velocity is, the more obvious the pressure difference among different pressure-sampling positions of the pipeline is and the more serious the deviation of calibrated K-factor from normal value is. So, when the calibrated K-factor deviate greatly at large flow velocity points but linear at other flow velocity points, the correctness of the pressure-sampling position in the calibration process should be considered.