USING
You just plug it in, and plug the device into it and it starts working. It is a little hard to use directly without combining it with a separate power strip or extension cable. For example, it is awkward to read and might not fit if you plug directly into the existing socket in a power strip or wall outlet. It is much easier if you buy a separate power strip, plug this on top of it, just swap in by the power trip extension and device into this. Then you can easily fit anywhere, can tilt and read more easily, etc. In poor lit areas, you will need to carry a flashlight to help read the screen. I just run around with a paper, pencil, and flashlight and write down findings while testing a number of devices in a row. Just swap out an existing plug, hold reset for 5 seconds to start fresh, and you're off and just monitoring the results. Measuring is actually very quick if you are just testing current operating state of things. It only takes a minute or so to swap out, check current wattage and cost, and move onto the next plug. I test items individually plugged into a power strip under a desk in less than 10 minutes -- swap each, power on, reset, cycle through measurements, write down finding, move on.
RESULTS
It immediately tells you current voltage, watts in use, amps, Hz, and a few more, and then projects the costs per hour, day, week, month, and year based on what it has seen so far. You can enter your own utility rate in case you run at a high bracket. It keeps a running total in KWh, total cost so far, so to isolate a new device you hold reset for 5 seconds. If you want the total cost while operating in a certain mode such as to isolate when running at full power you just hit the reset and it assumes costs from that point on and assumes if it keeps running at that it will project out. So you can easily calculate after resetting the cost per hour. For example, how much your computer uses while on and doing intensive work, versus sleep mode, versus turned off. It is nice to know how much per hour something costs so you might think twice how long you run it in that mode. Then you can leave it on for a day or two to discover the realistic cost such as how much it affects your monthly energy bill overall. For example, my water distiller cycles and while cost per hour is one thing, I want to know how much I am really consuming per day and per month.
EXAMPLES
For example, I learned my space heater uses 1100W at at my utility rate of 0.34/KWh I know it costs me 0.35/hr to use, so now there is a concrete cost that I know. My desktop computer consumes 100W while idle, but my laptop consumes only 30W while idle. My older computer speakers use 5W whether on or off it makes no difference with the power adapter plugged in. My external hard drive draws about 5W while off too. My coffee maker surprisingly uses 6W while off, 6.8W while on, which adds up to $17.80/yr just to sit on my counter while off. Now I will put it on a power strip. Under a longer test for something that cycles, my water distiller, it realistically costs $25/month, which makes me rethink how much I draw from it. I learned my new wireless printers each draw 3 to 4W while in standby mode, but 0W while off. I use them infrequently, so I might as well just turn them off while not using them.
DRAWBACKS
There are a few things that could be slightly better, but are all workable.
1. I had to build my own dongle by attaching this to a power strip for easier swapping & reading. (cheap & easy)
2. Need a flashlight to read in low lit areas due to no back light (no big deal really).
3. Long running tests sometimes reset, or automatically at 99:99 rather than remembering only the most recent 99:99. So if you check it shortly after it rolls over or resets, it will not be accurate. (but sometimes works)
The biggest problem is #3. I wanted to get an idea of a weeks worth of actual use of my water distiller because the daily use varies and would even out over a week. But I checked it after it reset or rolled over and then only had 8:22 of history in which it had not even run in those hours making it calculate that it was free. But now that it is back up to 47:00 in history it calculates $25/month. I don't know for sure the cause of why it reset other than it was around 99:99, but this hasn't always happened. I have since tested beyond 99 in which it lists "142h". If it did reset at 99:99, I wish rather than a complete reset every 99:99 that it would just drop the oldest data and keep rating the most recent 99:99 once it reaches that much. For example, I can't possibly test my water softener for a month this way in which I have no idea when or how often that runs so that a 99:99 sampling will not be adequate. Or else it just sometimes resets on me near that time. But really this is minor. I use it much more often for spot checking things.