When I was in the Middle East interviewing natural gas and oil companies, one issue that came up repeatedly was how often they should pull their ultrasonic flowmeters out of service for recalibration. Since that time I have raised this question a number of times in different contexts, and have discovered that there is no generally accepted guideline for this. I have spoken to members of the American Gas Association (AGA) 9 Committee, but they don‚Äôt seem interested in taking up this matter. I would like to assemble some guidelines for determining how often an ultrasonic flowmeter needs to be recalibrated. Some countries have adopted their own rules. The consensus seems to be somewhere between three and seven years, but this is quite a range. Also, some people say there are tests that can be run to determine if an ultrasonic meter needs recalibration. What are these tests? I welcome any thoughts on this topic. Thank you.