is for the client. Also these mineral reserves are taxed based upon energy content. The inert gases such as nitrogen have no value. (Some inert gases actually have negative value, most notably carbon dioxide and hydrogen sulphide, as they require extra equipment to remove from the natural gas, and costs are incurred in their disposal.) Other input parameters include contract hour as well as location latitude and altitude above sea level, isentropic exponent and type of materials used in the metering device to optimize the accuracy of calculations. In summary the gas flow computer requires approximately 30 initial input parameters in conjunction with "near realtime" gas flow, pressure and temperature sensing. In addition to providing volumetric, mass and energy flow data, the gas flow computer also provides date and time, instantaneous, hourly and daily data. The gas flow computer typically stores date/time stamped volume records in RAM for up to 35 days in order to provide sufficient time for a host system to retrieve the records as well as to allow time for human intervention if this retrieval fails to occur. The flow computer generally tracks modifications to flow parameters (e.g. orifice plate size or gas analysis data) in an "Audit Trail" that identifies the modified parameter, the time and date of the value change, the old and new values, and may identify the person making the change. The data log format and contents vary slightly by flow computer manufacturer, with all manufacturers designing to a specification outlined by the American Petroleum Institute. Flow metering accuracy is easily compromised if there are liquids in the gas stream. Therefore methods are implemented to remove liquids from the gas stream before measurement. However a newer V-Cone technology (the inverse of orifice plate technology) is being used to more accurately meter gas that contains some liquids. See also AGA-8 AGA-3 American Gas Association Landfill gas monitoring NX-19 Notes and references External links http://www.sgc-valid8.com -- Free online Flow Measurement Calculation and Verification Engine https://web.archive.org/web/20080828212148/http://www.squinch.org/gas.html -- Provides working hands-on examples of AGA 3 (orifice meters), AGA 7 (turbine meters) and AGA 8 (compressibility) gas flow calculations. http://www.aga.org/ -- website for American Gas Association, publisher of AGA report no. 3 (Orifice Meters), report no. 7 (Measurement of Natural Gas by Turbine Meter) and report no. 8 (Compressibility Factor of Natural Gas and Related Hydrocarbon Gases) http://www.api.org/ -- website for American Petroleum Institute website, publisher of the