A Pitot tube is a device invented by Henri Pitot (1695–1771) in 1732 and widely used in fluid dynamics for measuring the rate of flow of gases or liquids. For liquids, the device used is generally a manometer, with one open end facing upstream and the other end out of the stream. The different pressures at the two ends cause a liquid to shift position within the two arms of the tube. For gases, a Pitot tube is generally L-shaped, with one end open and pointing towards the flow of gas and the other end connected to a pressure-measuring device. This compares the pitot-tube pressure with the static stream pressure, the difference being a measure of the fluid velocity. This type of pitot tube is commonly used as an air-speed indicator in aircraft.