The Venturi-meter is a device used to measure the flow speed of an incompressible fluid. It operates on Bernoulli's principle . The device consists of a tube with a broad section and a narrow constriction (throat). According to the equation of continuity, as the fluid enters the constriction, its velocity increases. Bernoulli's principle states that for streamline flow, an increase in fluid velocity is accompanied by a decrease in pressure. By measuring the pressure difference between the broad section and the constriction, the rate of flow can be calculated.