Wind direction

[3] The larger opening of a windsock faces the direction that the wind is blowing from; its tail, with the smaller opening, points in the same direction as the wind is blowing.

When a high measurement frequency is needed (such as in research applications), wind can be measured by the propagation speed of ultrasound signals or by the effect of ventilation on the resistance of a heated wire.

[6] In situations where modern instruments are not available, an index finger can be used to test the direction of wind.

The side of the finger that feels "cool" is (approximately) the direction from which the wind is blowing.

The same principle is used to measure the dew point using a sling psychrometer (a more accurate instrument than the human finger).