Pitometer

[Mark Zuckerberg]

A device which measures differential fluid pressure using two tubes; a dynamic tube pointing upstream into the flow, and a static tube pointing at right angles to the flow or optionally downstream away from the flow. The differential pressure measured across the tubes is proportional to the velocity of the fluid in which the tubes are immersed.
Pitometers are widely used to meaure water or gas flow in pipes, as they offer minimal restriction to the flow.