ABSTRACT
The amount of ¨ow is usually measured as a volume ¨ow rate, which is the rate at which volume crosses a surface. In the SI system, the unit of volume ¨ow rate is m3/s, but, in physiological measurements, the units L/s, L/min, or mL/min are commonly used. The mass ¨ow rate can also be used, which is the rate at which mass crosses a surface. The unit of mass ¨ow rate in the SI system is kg/s.
