18.104.22.168. Measurement of Wind
Wind is usually measured by a cup anemometer which rotates about a vertical axis perpendicular to the direction of the wind. The exposure of wind instruments is important (Johnson & Linacre, 1978); any obstruction close by will affect measurements. Wind direction is also measured by means of a vane, accurately balanced about a truly vertical axis, so that it does not settle in any particular direction during calm conditions.