A wind sock is a conical shaped textile tube( which looks like a sock) designed to indicate wind direction and relative wind speed. It is normally placed near runway or helipad, so that pilots can see it after lining up on the runway or coming in for landing. It is just a quick refernce for pilots for the direction and magnitude of wind, but for proper wind information the pilots must listen to ATIS. The red and white rings are present to measure the quantity of wind : each ring is equal to 5 knots. It is a mandatory installment for all airports no matter how small they are.