Electronic gas measurement auditing or EFM auditing is a very important process in the natural gas industry. Within the last twenty years, the natural gas industry has changed from the dry flow chart recorder to the Electronic flow Computer(EFM) as the primary method of recording the measurement data for custody transfer.
These flow computers are still typically connected to an orifice meter and are subject to all of the problems in the primary device that a chart recorder was. In addition they have their own set of problems that crop up in the flow computer and transmitters, some of which had similar problems when it was a chart recorder and some of which are unique to the flow computer. Careful review of the meter data should still be (and usually is) a part of the monthly close process.
Even with the review process, occasionally measurement errors make it through to the payment calculation. It is for this reason that auditing is necessary and prudent. A proper audit procedure can be cost effective and ensure that proper credit is received for any delivery. As a side benefit, it will also help ensure that internal measurement is being performed properly