When I saw this thing on Amazon, I thought it was the coolest thing ever, a USB tester plus a multimeter, plus a thermometer in a tiny package. In fact, the product does what it says it will do; the problem is paying close attention to what the product description actually says it will do, and not listening to your expectations of what it should do.For example, it's a voltmeter. It can accurately measure voltages between 3.6 and 35 volts. Just take the supplied probe, plug it into the input, and put the alligator clips to your battery -- oops, your 1.5 volt battery can't be measured, but you can check those 3.7 volt lithium ion batteries. I did test the voltmeter against a quality digital multimeter, and the two tracked to the 2nd decimal place. So while it won't replace your dedicated multimeter, you can check that 12V battery on the trolling motor. It doesn't do AC.It's an Ohmmeter. But the range is only 1 to 999.9 Ω, which is very limited compared to a dedicated multimeter. Also it can't really measure 1 Ω. If you tried, you'd trigger the overload protection (been there, done that with a 2.2 Ω resistor). To use the Ohmmeter, connect the input to a USB power source. The input voltage is applied to the test leads on the output side, so if more current is drawn than the USB tester allows, it shuts down. Also, the ohmmeter is extremely inaccurate. I connected a 120 Ω 1% resistor (checked with a digital multimeter as correct) and the USB tester said it was 144 Ω. Notice that the product description says nothing about the accuracy of resistance measurements.There's one other problem with resistance measurements: the display of the resistance value is tiny and blue against a black background. It's hard to read even with a magnifying glass because is so dim. The other values, although tiny, are in lighter colors. This doesn't show in my photo because the camera is compensating for the lack of brightness; however since the tester is basically useless as an Ohmmeter, the problem isn't all that serious in and of itself.The supplied USB to alligator clip probes make it easier to connect USB to a real multimeter.I took some time to explain how the voltmeter and ohmmeter functions work. That's because the instruction sheet says nothing about what to do with the probes. The instruction sheet is less than helpful, and explains little. If you can figure out how it works on your own, then parts of the manual start to make a little sense.The USB tester is supplied with a tiny micro USB adapter. Upon close inspection I found that it adapts micro USB to USB-A (there is already a USB-A input and output). The manual says "If the Micro USB port is not plugged into the attached small adapter, the tester cannot be used on a USB-C device." The reader is invited to inspect the accompanying photo showing the tester happily testing a USB-C device, a wireless keyboard that charges via USB-C without the adapter plugged in. In another place the manual gives you a hint by adding the letters PD. By searching the web, I found that this is short for "Power delivery" and what is actually going on is that this supposedly triggers a higher current dynamic charging mode for USB-C devices. I'm going to try really hard not to lose the tiny adapter, although I guess any micro USB cable would suffice. The instructions just don't explain what's going on.Oddly, while there is a Micro USB input, the instructions say not to test Micro USB cables.The manual also says, "When you plug in the charger, it is a Chinese interface. You can switch to the English interface by pressing the button." The display doesn't default to Chinese.My photo also shows a fit and finish problem -- the display is crooked. I did not actually notice this until I looked at the picture. The display is really quite small and it can be awkward to read plugged into a device that you can't get your head near, like behind a desktop computer. You really could benefit from having a nice long USB-A extension cable.There is a display button. Pressing it displays other panels of data not discussed by the manual. One of them shows voltages on other USB pins besides the main power pins. The instruction sheet ignores most of them except 3 that are for settings (none of which in my opinion should be changed).As for testing USB charging, it seems to work fine. You could find out the capacity of that USB charger battery pack, although, inexplicably you have to do some multiplication to get the right answer -- haven't quite gone through that. I got it to look at the current drain of some of my USB-charged devices, in particular portable radios that have rechargeable batteries. I'm also interested in the output of solar USB panels on emergency radios. It should do well for comparisons, but I wouldn't trust the accuracy given my experience with the Ohmmeter. I would have given this tester a higher score if it had a decent manual and didn't try to sell itself as a multimeter. It's a good USB tester with a nearly useless multimeter function, weighed down with a bad manual.