Wind speed matters for everything from sailing to storm warnings. An anemometer is the instrument designed to measure it. The most familiar type uses three or four cups that spin on a vertical shaft; the rotation rate translates directly into speed.

Other designs include propeller styles that also indicate direction, hot-wire sensors for research, and sonic devices that calculate speed from sound-wave travel time. All must be mounted in open locations free of obstacles that distort the flow.

Weather stations, airports, and research towers rely on calibrated anemometers. Gusts, sustained speeds, and averages all come from these instruments. In high winds the cups can spin so fast that special high-range models are required.

Data from anemometers feed directly into forecasts and aviation reports.