Without a doubt, the main advantage of this handheld cup vane air velocity meter is that it doesn't need to be held exactly in the direction of the wind. Air velocity meters with impellers typically have to be held exactly in the direction of the air flow to take accurate measurements. However, this cup vane air velocity meter's system is so sensitive that it responds to the smallest of air currents. To perform a correct measurement with the PCE-A420 cup vane air velocity meter: First turn the meter on, then hold the meter vertically so the cups can rotate until the wind velocity is displayed. In the following picture you can see how to measure wind speed with the PCE-A420 cup vane air velocity meter.