how do they determine wind chill factor?

Answer 1

Well, it's been a while, so I had to do some research. If the wind speed is 25 mph & the temperature is - 6 F , the wind chill , or feel like temp. would be - 52.7 F. I found a site with a tutorial on it. This link is just one part of that page. It's a chart with temps. + wind-speeds :
http://www.mste.uiuc.edu/dildine/tcd_files/program1.4htm#table

Answer 2

Even when it is cool your skin has moisture on it . When the wind moves the wend near the skin will evaporate the moisture. U will get a loss of 60 calories for each cc. that is evaporated.