Positive displacement flowmeters have been the traditional choice for residential and commercial
natural gas flow and water flow measurement in the United States (a simple application of custody
transfer flow measurement, where the fluid being measured is a commodity bought and sold). The
cyclic nature of a positive displacement meter lends itself well to total gas quantity measurement
(and not just flow rate), as the mechanism may be coupled to a mechanical counter which is read by
utility personnel on a monthly basis. A rotary gas flowmeter is shown in the following photograph.
Note the odometer-style numerical display on the left-hand end of the meter, totalizing gas usage
over time