UPDATE: I ordered another anemometer from a different manufacturer, not much more expensive, WAY BETTER! And... in includes HUMIDITY too! (Video soon!)
This worked correctly the first time... but if you cycle through the menu and go back to the original settings, it loses its calibration or has some other failure. A reading of 10mph will show up as 1.0 mph and driving in my car at 25 mph showed 2.4 mph. I returned the unit... the new one did the exact same thing.