A flow meter is an instrument used to calculate the flow rate (quantity) of a liquid or gas moving through a pipe. They have diverse applications, and come in a variety of types for each different purpose. Volumetric flow meters measure the volume of fluid passing through the equipment. A velocity flow meter can measure the velocity of the flowing streams in order to determine volumetric flow (magnetic, turbine, and ultrasonic are all examples of velocity flowmeters). Mass flow meters measure the mass flow of the flowing stream (ex: Coriolis and thermal flow meters). Inferential flow is the process of determining flow by inferring its value from other measured parameters (ex: differential pressure, target and variable area flow meters).