This is Not How Anemometers Work // Who started this false explanation? 

Most have only 3 cups. They are cheaper to make .

Thank you for your nice comment.

I appreciate your comment. Best regards.

@@JimscoolstuffThanks for answering! Now that I have your attention, let me ask you a question: how do you calibrate an anemometer? The most obvious method is with another anemometer. But what if you want to validate the calibration without another anemometer?

@@gustavoenriquejimenez8098 The way available to most people is a vehicle with a speedometer; however, the unit being calibrated must not be near the vehicle. The way that I did it years ago was to use a long pole arranged perpendicular to the front of the vehicle, and of course at a time with no wind. I used a pole 10 feet long (3 meters) so that the unit was in front of the vehicle. This is probably illegal most places, but I was young and daring then.

@@Jimscoolstuff Ok, thank you! I will try that, in a safe location.

They must be calibrated. You can not assume that the cup is moving at the wind speed.