MEASURED through the difference in pressure from the upstream side to the downstream side of a partially obstructed pipe.In the Venturi Tube, the fluid flow-rate is measured by reducing the cross-sectional flow area in the flow path, generating a pressure difference.The pitot tube measures the fluid flow velocity by converting the kinetic energy of the flow into potential energy. It measures fluid flow velocity by DETERMINING the stagnation pressure and static pressure.Venturimeter and orifice meter are DIRECTLY used to measure the discharge of the flow through the pipes. However, the pitot tube MAY be used to measure velocity and then the discharge of the flow indirectly. Anemometer An anemometer is a weather monitor instrument used to measure wind speed.Basic Principle of Hotwire AnemometerWhen an electrically heated wire is placed in a flowing gas stream, heat is transferred from the wire to the gas and hence the temperature of the wire reduces, and due to this, the resistance of the wire also changes. This change in resistance of the wire BECOMES a measure of flow rate.∴ Hot wire anemometer is used to measure the velocity of the fluid.