Btu (mean)
Btu (mean) is a unit of energy used primarily in the United States defined as the heat required to raise the temperature of one pound of water from 59°F to 60°F under standard atmospheric pressure.
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.