Pinwheels are pretty optimized from a design standpoint, and are so cheap and easy to build that putting a pinwheel to work as an HVAC duct flow meter ... custom cut from patterns scaled down ...

The first step is to cut a piece of duct ... take off the duct tape, soak the wart in warm water and file off the dead skin with a pumice stone or emory board. Then leave the duct tape off for ...