An anemometer measures wind speed (or your speed, if you're moving and the air is standing still). We have a small hand held digital one that also measures temperature. It seems pretty accurate (or at least, it agrees with itself) but we haven't calibrated it.

To turn it on you press and hold the button for a while. To turn it off you do it again. (Or just wait?)

You have to be careful you hold it so the air flows through it. If you twist it at an angle the reading goes down.