Q: Why is this device power usage so much power and with such variation? I just got a wattage meter to try to get a sense of where my electricity usage is going. One of the surprises was my cheap drugstore humidifier, which seems to be drawing 640 watts. I have a huge basement dehumidifier that's only using 240 watts and substantial power tools that use even less.
The other strange thing is that the humidifier power usage jumps around dramatically. I made an animated gif of the usage, but it's too big to paste inline, so here's a link:
https://www.dropbox.com/s/185m6o45ja6d6z7/humidifier-power.gif?raw=1
What it shows is the usage jumping constantly and widely, from 640W all the way down to 610W, just in a few seconds. It varies even more widely over longer observations.
So why is this little appliance using so much power and with such wild variation? Could it be defective, or even dangerous?

A: If your watt meter is crappy, it won't take into account power factor (but then I wouldn't really call it a wattmeter anymore since the whole point of a wattmeter is to see through the power factor). I kinda doubt your drugstore humidifer is drawing 640W. 
You can't calibrate it. Voltage and current have to be in phase for real work to be done. When they are out of phase you get reactive power which is just real power moving back and forth not doing any work. To measure this it has to measure instantaneous voltage and current instant-to-instant. If your meter just measures voltage over time, and current over time, and then uses those two numbers to calculate power then it ignores the phase information.
It is like a warehouse that has imports and exports. If your imports and exports are staggered then your warehouse isn't ever really overfilled. But when not staggered you get a multiple consecutive import shipments accumulating in your warehouse before an export shipment can empty it out again. But you cannot see this effect if you just examined the average number of exports vs imports over a long period of time such as year or month. The phase information between imports and exports is not accounted.
