From Glossary of Meteorology
(Or Pitot-static tube.) A pressure anemometer consisting of two concentric tubes that are oriented parallel to the flow.
The inner tube is open at the upstream end to sense the total pressure, while the outer tube is closed with a rounded contour and has a ring of small static pressure ports a short distance downstream. Each tube is connected to a manometer and the difference between the two pressures, the dynamic pressure, is proportional to the square of the fluid speed.