A few facts:* I am only talking about the "AC 100A Meter(Split Core Transformer)" style; the other 3 styles you can order from this page look dramatically different and no doubt have extremely different functionality, so don't rely on customer reviews or answers that do not specify which style they bought; also, it is probably a good idea to specify the style you are considering purchasing if you are asking a question on here. (Or not, you decide.)* You will have to supply your own leads to connect directly to the power source. The wires and alligator clips you see in the pictures are my own.* CONCLUSION: Don't. Assume. Anything. Ever.A few opinions:* NEGATIVE: This meter does not keep track of the amount of time that has passed since the watt-hours were reset, so you will have to mark down the time somehow if you intend to calculate daily/monthly energy costs.* POSITIVE: This meter survives power outages without losing track of watt-hours used, which every power meter should do and is a huge benefit in areas like mine where the power goes out frequently and I cannot monitor the power daily.* CONCLUSION: Just buy a couple of these and you'll be happy you did.* NOTE: I live in very rural Florida, USA--notice the electobraid in the pictures which implies that I have horses grazing in my front yard--so code violations and permits are basically non-existant. So, please don't leave comments regarding code violations from my pictures or assume that I was the person who made them. Also, please don't flame me because you assume to know my political persuasion: My family is divided politically and religiously (it would blow your mind if I explained it all), and we still get along super-well because we all love and respect one another, thank you very much. This posting is about electrons, not people.220-volt measurements:* I saw conflicting answers regarding the measurement of 220-volt (or 240-volt... whatever, I get it) in places like the United States where there is a neutral wire that divides the voltage in half. My use case is a main panel that supplies power to a sub-panel in my workshop where some circuits are 110-volt and some are 220-volt. (NOTE: The voltage between the red and black wires is 220 volts, and the white wire is the neutral that is halfway in between. Thus, red to white is 110 volts and black to white is 110 volts, albeit at opposite phases but what the heck the appliances are stupid and don't really care about phases.)* I have 3 of these devices, so I am able to show my results in real time. Ignore the watt-hour numbers in my photos, because the meters were reset at different times. Pay attention only to the volts, amps, and watts. (I'll look it up later so I become a supposed expert, but right now I really do not understand what power factor even means. I am pretty smart and was literally at the top of my class in my 300-level college electronics course, so I know what I know and I know that I don't know everything.)* Everybody who answered the question about measuring 220 in this situation (at the time I read it) agreed that you should put the power leads on both ends (red and black) of the 220 circuit, so in all 3 samples the power leads stay in the same place.* Of course, if you have an appliance (like my air conditioner or my well pump) that only uses 220 and doesn't use the neutral line at all, you could simply span the red and black wires and ignore the white wire. But for subpanels where there is a mix of these appliances and circuits, this is not so simple.* Results when the coil was on the black side (and the #3 power leads were spanning the red and black): * #1 black-side meter (left): 120 V, 5.2 A, 585 W * #2 red-side meter (right): 122 V, 0.3 A, 22.5 W * #3 red/black meter (middle): 242 V, 0.3 A, 46.1 W * #1 PLUS #2 = 607.5 W, not 46.1 W!!!* Results when the coil was on the red side (and the #3 meter power leads were spanning the red and black): * #1 black-side meter (left): 120 V, 5.5 A, 615 W * #2 red-side meter (right): 122 V, 0.3 A, 22.5 W\ * #3 red/black meter (middle): 242 V, 5.6 A, 1.25 kW * #1 plus #2 = 637.5 W, not 1.25 kW!!! (OMG, Becky!)* Results when the coil was on the white side (and the #3 meter power leads were spanning the red and black)... what the heck, this sort of answers the question of whether current flows on the neutral or not (SPOILER ALERT, it does, why else would it be made of copper): * #1 black-side meter (left): 121 V, 5.3 A, 593(5?, thanks Siri!!!) W * #2 red-side meter (right): 122 V, 0.3 A, 22.6 W * #3 red/black meter (middle): 243 V, 5.1 A, 1.16 kW * #1 plus #2 = 617.6 W, not 1.16 kW!!!* CONCLUSION: It is unpossible to accurately measure a split voltage system with a single meter. If you put the coil on one end (black) or the other (red) you will get the correct amperage for that side but it will inaccurately multiply that by the total voltage and overstate the watts. If you put the coil in the middle, you will get the larger of the two amperages from either side multiplied by the total voltage and (IMO) overstate the watts (maybe?).* QUESTION: My dad always told me you "pay" for the other side even if you're not using it, so you should balance out the 110-volt circuits as much as you can to maximize your cost. Is that true?* OBVIOUS CONCLUSION: I have gone to all the trouble of buying 3 units and giving you all of the facts (backed by photos), so you should not give me a thumbs down even if you completely disagree with anything I have said. You should give me a huge thumbs-up and politely state your disagreements with me to make yourself feel better, look smart to everyone else, and actually educate me in the process.Thanks, and G-d bless.