Myself writes: “So, you’ve sealed all the gaps in your home’s skin, added insulation in all the right places, and maybe taken the plunge on some new windows. An energy audit is the next step to efficiency, and the Kill-A-Watt is an affordable way to get started.
“It shows you the voltage and frequency that the power company is delivering, and measures the amount that your appliance draws. It tells you amps, watts, Volt-amps, and power factor. (At DC, watts and VA are the same thing, but in AC, a phase lag between the voltage curve and the current curve causes non-unity power factor, which is why your computer’s UPS might be rated to drive 700VA but only 450 watts.) Having this information is essential for UPS sizing, energy planning, and circuit troubleshooting.”
“For data geeks, there’s also the Watts-Up, a more expensive instrument that includes more advanced datalogging: http://www.doubleed.com/”
Froogle turns up the Kill-a-Watt for $20 to $25 all over, though Myself noted that it’s available via a place called “SuperMediaStore” for $19 ($24 minus $5 with the code “silverbells”) and free shipping. That’d beat the deals we found.