Well, to put it as simply as possible. It works more like a standard whole house meter in the sense that it keeps a running total KW usage from the time you plug it in and the same button will alternate between a hr/min counter and total KW usage. So, with a little basic math you can take the total KW usage, say 240KW, divided by the total time, say 24hrs. You get 10KW/Hr, that's a total of whatever the device your measuring uses per hour. The longer you leave this plugged in the more accurate your total will be since most electrical device's power usage fluctuates slightly while they are running. Take the rate you pay for electricity, say $0.09 and multiply it by your KW/Hr usage. You get $0.90 per hour, that's what your device costs you to run per hour.
Hope that helps. If you want it to do the math for you, you need to get a much more expensive meter. As I stated in my last review, I don't recommend this meter for extreme long term metering. Or testing high usage devices such as heaters, coffee makers, etc.. Again if you want to do those things, you should invest in a more expensive meter. This is great for simple quick tests just like a cheap multi-meter would be.
This measures the immediate power consumption of your appliance. I needed to know what my computer, monitor, printer, cable modem, voi moden, external hard drive was pulling in order to get the correct battery bavkup.
This is just a guess, but probably is correct. My guess is that there power level counters (64-bit, or 128-bit, or...) which are incremented off of the internal processor clock and that an interrupt is generated every so many clocks and at that time the counter is checked and a subroutine determines the appropriate consumption for day, week, month, ..
this thing tells you how many watts something uses so that you can find out how much something costs by the day, week, month, year, but no there is not a clock that does it for you, and the price for power can change too, so the math part on costs is up to the individual to figure out. I found the average costs for certain appliances by looking it up on Google and went from there. for example, running 700 watts for 12 hours a day all month, should average at about $35 a month, last time i checked.
It is understood that one can calculate the consumption. However, the product information is misleading. With the current technology, use the clock and the battery is very cheap. You could enter a date and store the counter in the absence of energy supply. I bought this unit and I'm disappointed.
When you plug it in it tracks the length of time and the power consumption. BEFORE you unplug it, write down the hours and power usage, then divide to get the per hour, per week or per month usage total that you want.