A fluid flow-measuring device that consists of a tapered tube to form a throat such that the increase in velocity results in a decrease in pressure, known as the venturi effect. The differential pressure produced by the flowing fluid through the throat gives a measure of the rate of flow. The pressure differential can be measured using manometers or other types of pressure measurement devices attached both upstream and at the throat. In practice, the theoretical rate of flow through the device is not achieved as friction in the device is ignored. To allow for this difference, a correction factor known as a coefficient of discharge is used. For a well-designed venturi, the coefficient lies between a value of 0.95 and 0.98. It is named after Italian physicist Giovanni Battista Venturi (1746–1822).