Degree days are measured as the number of degrees above or below a standardised temperature on any given day. In winter, US traders track heating degree days week by week, or month by month, normally against a standard temperature of 65F, on the basis of how many degrees of heat are required to bring municipal office buildings up to this temperature. Five days of heating by 2 degrees, for example, equals 10 heating degree days. In summer, the market tracks cooling degree days.