The SONARtrac® flow meter operating principle is based on sensing pipe deformation (which is strain in the pipe wall) produced by dynamic pressure fields traveling at the average flow velocity in the pipe. Pipe deformation or strain is also produced by mechanical vibration and acoustic ‘noise’ traveling in the fluid and/or the pipe wall. The ability to make a flow measurement depends on the relative levels of the flow-generated strain compared to the vibration/acoustic-generated strain, which reach the sensors mounted on the exterior of the pipe. In general, lower vibration/acoustic strain levels and/or higher flow-generated strain levels permit operation at velocities near or below the 3 feet/second guideline.