Take the bargain bin multimeter and pop off the clear plastic, paint whiteout on the numbers but keep the dashes. Set the multimeter to DC mA and spin the rotor to see how it works. Now you can mount it to a broomstick and have someone drive you down a back road on a still night while you hold it out the window to calibrate it. Take a sharpie permanent marker and mark dashes on the multimeter. Snap the clear cover back into place and mount your new anemometer.