You don add a degree sign (or any other unit) after the number used for wind chill or for the humidex. Why is that?
This is because the wind chill and the humidex are indices and not physical quantities. In other words, these quantities are calculated, not measured. Even though these two indices are calibrated according to the Celsius temperature scale, we do not put C after their values to emphasize the fact that they are not temperatures. Note: In imperial units, the wind chill and the humidex indices have different values because, in these units, they are calibrated according to the Fahrenheit temperature scale.
