Calories (15 °C, NBS 1939)
The 15 °C NBS 1939 calorie is the amount of energy required to raise the temperature of one gram of water by one degree Celsius, from 14.5 °C to 15.5 °C, at standard atmospheric pressure. This specific definition was established by the National Bureau of Standards (NBS) in 1939.
Therm (EC)
The therm (EC) is 100,000 Btu (International Table), or about 105.5 megajoules (MJ). Gas in the United Kingdom was historically billed in therms, and the EC stands for European Community, to tell it apart from the US therm.