Ergs
An erg is a unit of energy defined as the work done by a force of one dyne exerted over a distance of one centimeter which is equivelent to 10-7 joules.
Btu (3.9°C)
The Btu (3.9°C) is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit at the temperature where water reaches its maximum density which occurs at approximately 3.9°C (39°F).