The American Gas Association defines the orifice meter as the complete measuring unit consisting of a primary and a secondary measurement device. The orifice meter body, tube and orifice plate are considered the primary measuring device. This primary device is equipped with pressure taps that allow for the hook-up of a secondary device to sense the output signal of the primary orifice meter. The secondary device is some type of recorder or datalogger that allows for the recording of the events (i.e. signal levels and changes) that are created in the primary device