A gas meter is a specialized flow meter, used to measure the mass or volume of Natural Gas. Gas meters are used at residential, commercial, and industrial buildings that consume fuel gas supplied by a gas utility or by the automobiles. Gases are more difficult to measure than liquids, because measured volumes are highly affected by temperature and pressure as well as gas composition. Gas meters measure a defined volume, regardless of the pressurized quantity or quality of the gas flowing through the meter. Temperature, pressure, and heating value compensation must be made to measure actual amount and value of gas moving through a meter. This kind of volume are called as uncorrected meter volume. To correct the uncorrected gas volume, Flow computers or electronic volume corrector are being used.
Several different designs of gas meters are in common use, depending on the volumetric flow rate of gas to be measured, the range of flows anticipated, the type of gas being measured, and other factors.
An adequate Gas meter measures gas quantity flow from the system at standard condition with its error limits and factors.

A gas chromatograph is a chemical analysis instrument for separating chemicals in a complex sample. A gas chromatograph uses a flow-through narrow tube known as the ‘column’, through which different chemical constituents of a sample pass in a gas stream (carrier gas, ‘mobile phase’) at different rates depending on their various chemical and physical properties and their interaction with a specific column filling, called the ‘stationary phase’. As the chemicals exit the end of the column, they are detected and identified electronically. The function of the stationary phase in the column is to separate different components, causing each one to exit the column at a different time (‘retention time’). Other parameters that can be used to alter the order or time of retention are the carrier gas flow rate, column length and the temperature. Gas Chromatograph checks composition of Gas flow from Gas meter. It is required to calculate gas quantity in metering system.  

Pressure transmitter and temperature transmitter are to record real time temperature and pressure.

A pressure sensor is a device for pressure measurement of gases or liquids. Pressure is an expression of the force required to stop a fluid from expanding, and is usually stated in terms of force per unit area. A pressure sensor usually acts as a transducer; it generates a signal as a function of the pressure imposed. For the purposes of this article, such a signal is electrical.

Pressure sensors are used for control and monitoring in thousands of everyday applications. Pressure sensors can also be used to indirectly measure other variables such as fluid/gas flow, speed, water level, and altitude. Pressure sensors can alternatively be called pressure transducers, pressure transmitters, pressure senders, pressure indicators, piezometers and manometers, among other names.

A flow computer is an electronic computer which implements algorithms using the analog and digital signals received from flow meters, temperature, pressure and density transmitters to which it is connected into volumes at base conditions. They are used for custody or fiscal transfer.

It also audits changes that have been made to any of the parameters required to turn the raw flow meter data into volumes. Its records events and alarms related to the flow meter (for example, loss of flow, loss of required electrical signals from measurement transducers, or transition of these electrical signals near their upper or lower range). It keeps a running tally of the volume for each flow meter it monitors and creates a record of this volume on an hourly, daily, batch or monthly basis. The flow data is made available externally through an electronic interface so that other computers can download the information for supervision, accounting and auditing. 

To process data of Gas meter, Gas chromatograph, PT & TT, actual gas volume calculate with correction factors.