Degree Days and Pushing Wrong Key

After proudly saying New York has a downtrend in degree days, while at the brewery, I was hit by a trick question: "Say, what is a degree day?"

Don't you hate people who question the assumptions behind assumed facts? Obviously, no one had any idea what a degree day was, which sort of took the wind out of my big unfurled sail. The mast snapped.

To the left is a "degree day meter" schematic.

A degree day, according to the always persuasive Wiki:

A degree day is a measure of heating or cooling. Totalised [Socialist Spelling] degree days from an appropriate starting date are used to plan the planting of crops and management of pests. Weekly or monthly degree-day figures may also be used within an energy monitoring and targeting scheme to monitor the heating and cooling costs of climate controlled buildings, while annual figures can be used for estimating future costs.

A degree day is computed as the integral of a function of time that generally varies with temperature. The function is truncated to upper and lower limits that vary by organism, or to limits that are appropriate for climate control. The function can be estimated or measured by one of the following methods, in each case by reference to a chosen base temperature...

never mind, let me find something that makes sense:

Heating degree days are calculated over a period of time (typically a year) by adding up the differences between each day's mean daily temperature and the "balance point" temperature of 18°C (or 65°F), above which the building is assumed not to need any heating (the actual indoor temperature will be higher due to insulation retaining heat from the occupants). Thus three successive winter days with average temperatures of 4°C, −2°C and −4°C totals to 56 HDD. Conversely, three summer days of 26°C, 28°C, and 30°C totals to 30 CDD. For differences between day and night temperatures, the average is taken; so a day maximum of 10°C with a night minimum of 2°C averages to 6°C, or 12 HDD.

The system has several problems. Heat requirement is not linear with temperature (Valor et al., 2001), and heavily insulated buildings have a lower "balance point": some will need heating below 18°C, but others won't need any heating until the temperature is much lower (see Superinsulation). Solar gain (see Passive solar) reduces the need for heating on sunny days (but not cloudy days), and wind increases it (by an amount that depends on how tightly the building is constructed). People also differ in their opinions about what constitutes a comfortable indoor temperature.

So, you will never see a reference to degree days from me again. Just rest assured, whatever it means, I am right.