Editing Wind chill (section)

=== Original model ===
Equivalent temperature was not universally used in North America until the 21st century. Until the 1970s, the coldest parts of Canada reported the original Wind Chill Index, a three- or four-digit number with units of [[kilocalorie]]s/hour per square metre. Each individual calibrated the scale of numbers personally, through experience. The chart also provided general guidance to comfort and hazard through threshold values of the index, such as 1400, which was the threshold for [[frostbite]].

The original formula for the index was:<ref>*Woodson, Wesley E. (1981). ''Human Factors Design Handbook'', page 815. McGraw-Hill. {{ISBN|0-07-071765-6}}</ref><ref>[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690003109_1969003109.pdf Aquation 55, page 6-113]</ref>

<math display=block>WCI=\left(10\sqrt{v}-v+10.5\right) \cdot \left(33-T_\mathrm{a}\right),</math>
where:
*''WCI'' = wind chill index, kg⋅cal/m<sup>2</sup>/h
*''v'' = wind velocity, m/s
*''T''<sub>a</sub> = air temperature, °C