Spink Controls offer an Industrial flowmeter used to measure flowrate of liquids and gases. It operated on the Variable Area Principle, where the fluid flow raises a float in taper tube increasing the area of passage of fluid. The greater the flow, the higher the float is raised. The height of float is raised by a combination of the buoyance of the liquid and velocity head of the fluid. With gases, the buoyancy is negligible, and float responds to the velocity head alone.