[sphelps]

According the producers of the energy monitor:

In AC power measurements, there actually three separate power components that can be measured:

Apparent Power: Measured in VA (volt - amperes). This is measured by taking the RMS voltage and RMS current readings and multiplying them together. This is what the eMonitor reports for power. All electrical circuits must be sized to handle apparent power because instantaneously, this is the maximum amount of power that can be flowing in a circuit.

Real Power: Measured in watts. This is the actual power that is being consumed by the load. This is what the utility company measures on the meter, as is what customers see on their electrical bill.

Reactive Power: This is kind of like imaginary power. It is really the difference between the Apparent Power and the Real Power. It is power that flows back and forth while the voltage and current are out of phase and is caused by the inductive load. Your utility company does not charge for reactive power, but it must handle reactive power, and reactive power does cause real current to run in your wires, and can generate heat. Reactive power is measured in VAR (volt - amperes reactive).