Many traditional flowmeter technologies respond to the volumetric flow rate of the moving fluid.
Velocity-based flowmeters such as magnetic, vortex, turbine, ultrasonic, and optical generate output
signals proportional to the speed of fluid molecules and nothing else. This means that if the fluid
flowing through one of these flowmeter types were to suddenly become denser (while still flowing by
at the same number of volumetric units per minute), the flowmeter’s response would not change at
all.