The link is an excel spreadsheet intended to simplify the comparison of clothing worn, in different weather conditions, with the relative comfort of the character. Some liberties have been taken ~ many of the clothing insulation modifiers have been adjusted for what I believe would be more accurate for medieval clothing. However, anyone using the document can easily change the variables as they wish.
The calculator then adds together the combined CLO (clothing insulation) for all articles worn. Then the user must input the temperature, in celsius. This then calculates the "ease": the amount of CLO necessary to be perfectly comfortable while at rest.
Then there are figures that indicate the amount of damage that a character will suffer if participating in that activity with their present "ease" for a 12-hour-period ~ that is, a day of travel or a night of sleeping/rest. Hit point penalties are indicated if it is too cold for the clothing that is worn or if it is too hot.
Moreover, there are three lines for calculating the effect of "heating up" while in combat. As combat goes on, characters will begin to sweat uncomfortably, to the point where they will begin to take damage PER ROUND in addition to all other considerations.
This is entirely optional, obviously, for anyone using the table for their campaign.