Measuring power with a simple voltmeter (radio shack) is very in accurate.
For most devices the voltage waveform and current waveforms are not in
phase.   That is why most devices now simply give VA and not watts --
easier for most individuals to comprehend.

I did a quick web search for power meters... this url looks like it might
be useful for those California list followers so inclined...:-)

http://energyoutfitters.com/powmeter.htm