Electron-volts
An electron-volt (eV) is used in the fields of atomic and particle physics. It is the amount of energy gained or lost by a single electron when it is accelerated through an electric potential difference of one volt.
Btu (15°C)
The Btu (15°C) is a specific variant of Btu to reflect the energy needed to raise the temperature of water at 15 degrees Celsius by one degree.