The spokes turn the shaft as the wind blows. The wind speed is indicated by the speed of the spinning shaft. In many other countries, they are stated in kilometers per hour. Wind direction is measured with an instrument called a weather vane. A weather vane has a broad, flat blade attached to a spoke pivoted at one end.
Wind blowing on the blade turns the spoke so that the blade lines up in the direction of the wind.
The wind direction may be indicated by an arrow fastened to the spoke, or by an electric meter remotely controlled by the vane. Wind directions are often indicated by using the 360 degrees of a circle. On this circle, north is indicated by 0 . Winds at various altitudes often differ in speed and direction. For example, smoke from a chimney may be blown northward while, at the same time, clouds higher in the sky are blown eastward.