the marked watt ratings on the device is likely more accurate than a clamp on amp meter.
quiet time at nite by using a inverter on your car for a couple of CF lights is a great thing.
if your really into getting a generator, buy 2:)
a large run everything high capacity one and a small 1000 watt quiet light weight fuel thrifty one.
my small generator gets used often, so does my 1000 watt inverter.
my 4000 watt generator has run once in the last 5 years