Hi Bahati. To measure windspeed accurately
- find something that can turn easily like a wheel from a toy bicycle or cart
- find three or four half balls, like the hollow plastic floats from a toilet or water tank cut in half, or the bottoms of plastic bottles
- fix the cups (half balls) on the rim of the wheel, facing around the rim the same way
- figure out a way to count the number of times the wheel turns a second - a counter and a watch is one way, and using an electronic bicycle speed counter is another
- calibrate by driving in a car at various speeds (like 10kmh, 15kmh etc.), and measuring the number of turns a second at that speed
I hope thats clear, and let me know if I can offer more advice.