The paper describes a new and unique design of a primary Gas Flow Calibrator. It is an automatically controlled precision volumetric flowmeter calibrating device specifically designed for use with a variety of gases over a wide range of pressures. The Aerotrak is a closed loop positive displacement system able to minimize both the quantity of gas used and the energy required to create the desired flow rate. The entire operation of the Aerotrak is under the automatic control of a uniquely programmed Personal Computer (PC). When initiated by the operator, the pre-selected program ensures the calibration data is taken after the pressure and temperature surge created by the initial piston motion has completely decayed and the flow rate is constant. This is achieved by the computer comparing successive calibration points and accepting data only when it has repeated within specified limits. As the actual data is being generated, it is continuously displayed for the test operator and stored in memory. Upon completion of the test, all data can be viewed on the computer screen by the operator and immediately evaluated. The completed data is then stored on a diskette which can be used to generate hard copy printouts and the plots of curves.