For any individual day, degree days indicate how far that day's average temperature departed from 65^oF. Heating Degree Days measure heating energy demand. It is a measure to indicate how far the average temperature fell below 65^oF. Similarly, Cooling Degree Days's, which measure cooling energy demand, indicate how far the temperature averaged above 65^oF. In both cases, smaller values represent less fuel demand, but values below 0 are set equal to 0, because energy demand cannot be negative. Furthermore, since energy demand is cumulative, degree day totals for periods exceeding 1 day are simply the sum of each individual day's degree day total. For example, if some location had a mean temperature of 60oF on day 1 and 80^oF on day 2, there would be 5 HDD's for day 1 (65 minus 60) and 0 for day 2 (65 minus 80, set to 0). For the day 1 + day 2 period, the HDD total would be 5 + 0 = 5. In contrast, there would be 0 CDD's for day 1 (60 minus 65, reset to 0), 15 CDD's for day 2 (80 minus 65), resulting in a 2-day CDD total of 0 + 15 = 15