Is there an easy way to figure out the wind-chill temperature?

Dear Tom,
Is there an easy way to figure out the wind-chill temperature?
— Stave MacFredrickson
Dear Stave,
A good approximation of the wind-chill temperature can be found by multiplying the wind speed by 0.7 and then subtracting that value from the air temperature. For example, if the air temperature is 20 degrees and the wind speed is 25 mph, use the formula
20 – (25 x 0.7) to determine that the wind-chill temperature is 2.5 degrees.
The actual wind-chill temperature calculated from National Weather Service tables is 3 degrees. The wind-chill temperature assumes a human face at a height of 5 feet above the ground on a clear night.
Wind speed magnifies the effect of cold temperatures. Cold air blown by wind increases the rate of convective heat loss from human skin much more rapidly than calm air.