Measurement in today’s natural gas pipeline systems encompasses many challenges. Measurement departments are faced with tighter system measurement balances than they were ten short years ago. Ultrasonic meters are the meter of choice to help with these challenges. Pipeline companies have pushed USM manufacturers to advance the USM technology to help with the challenges of measurement. Manufacturers have improved the ultrasonic technology greatly over the past 15 years. Many of these enhancements have been in the form of diagnostics and processing speed and power. This has aided measurement departments in reaching their goals of increased system balances and improved overall measurement uncertainty. Flow calibrating the ultrasonic meter is a vital part of the process. Most users require flow calibrations to improve meter performance and overall measurement uncertainty. The latest revision of AGA Report No. 9, Measurement of Gas by Multipath Ultrasonic Meters, Second Addition [Ref 1], requires flow calibration for ultrasonic flow meters when being used for custody transfer applications.