Windsock

Windsocks are used to tell wind speed and the direction of the wind speed itself. Windsocks typically are used at airports to indicate the direction and strength of the wind to pilots and at chemical plants where there is a risk of gaseous leakage. They are sometimes located alongside highways at windy locations.

Wind direction :

Wind direction is the opposite of the direction in which the windsock is pointing (note that wind directions are conventionally specified as being the compass point from which the wind originates; so a windsock pointing due north indicates a southerly wind). Wind speed is indicated by the windsock's angle relative to the mounting pole; in low winds, the windsock droops; in high winds, it flies horizontally.

Estimate the speed of the wind

Each stripe adds up 3 knots to the estimated wind speed,

• the first stripe indicates a 3-knot breeze;
• the second stripe indicates  a 6-knot wind;
• the third stripe indicates  a 9-knot wind;
• the fourth stripe indicates 12 knots;
• the last stripe indicates  15 knots or stronger wind;

in the end, these numbers are not standard and may be different depending on the windsock itself

References :

• FAA standards
• https://en.wikipedia.org/wiki/Windsock