Wattage usage

I was just thinking back to my time tinkering on computers, and people hooking theirs up to little wattage meters or something, basically you would plug your main computer power cord into this little thing about the size of a light timer, and then that little meter had another plug on the back, which went into your wall. Then it would read the pull. Anyone tried something like this on their growbox/growspace to see what sort of impact it should have on your overall household energy consumption?

heres another way to do it calculate the amount of hours per day your light is on... multiply that by the total wattage then multiply that figure with you kwh price (the price of electricity per kilowatt hour) and ya know how much per day it costs and uses.

That sounds good too. So you figure whatever it advertises it uses, that's per hour?