The use of orifices for commercial flow measurement has a long history dating back more than 50 years. Orifices are extensively used in the United States natural gas, petroleum and petro-chemical industries and are important as one of the most practical ways to meter large volumes of gas flow. These meters are very reliable and cost effective; and if properly used, can be relied upon to give accurate results. Proper use normally requires the steady flows for which orifices were intended and for which the orifice coefficients were developed. In actual field installations, flow is often not steady but subject to the periodic changes in pressure and velocity that are referred to as pulsation. Pulsation can be caused by compressors, pressure regulators, control valves, fluctuating loads, or by flow-induced phenomena within the piping. It is known and well recognized that pulsation causes errors in orifice meter results. In fact, A.G.A. Report No. 3 on Orifice Metering of Natural Gas, which is also API 14.3 and ANSI/ API 2530, clearly states that: “Reliable measurements of gas flow with an orifice cannot be obtained when appreciable pulsation . . . are present at the measurement point.”