A very unique feature of a Precision Balancer is it's ability to read wind speed.
This method can be as accurate as 2mph.
All you need is a Tachometer and a Balancer and a 11 x 8 Prop.

Place the prop on the balancer and either place the balancer on a level surfaced or hold it so that the BACK of the prop is facing the direction the wind is coming from.

Turn on the tach and read the wind speed. The wind speed with the 11x8 prop will be the RPM divided by 100. Most tachometers read rpm in thousands so the wind speed will be in tens. For example, a reading of 0.5 on the tach is 5 mph. A reading of 18.8 on the tach is 188 mph (in which case you should not fly).

The recommended prop for most accurate readings is a Top Flite 11 x 8 Power Point prop. Any 11 x 8 prop should work and be reasonably accurate, if you want to be more accurate use the following formula:-

Wins Speed (in MPH) = RPM x Pitch of the prop (in inches) x .00114