Simply plug the Kill-a-Watt meter into an AC receptacle and then plug the appliance into the meter. It will assess how efficient - or inefficient - your appliance is. A large LCD display with a count consumption by Kilowatt-hours, the same as your local utility. You can then figure out how much that appliance will cost to operate by day, week, month or year.
The Kill-A-Watt meter also allows you to check the quality of your power by monitoring voltage, line frequency and power factor.