I purchased this load tester several months ago when the dealer showed it to me, but forgot I even had it until last night, when I wanted to load test a sensor ground circuit. I followed the instructions, and it has you use it with a multimeter, and when testing ground, hook the ground lead to the circuit being tested, then measure at a +12v fuse, or battery terminal. I tested it at the battery terminal, and depressed the button for 10 seconds to load the circuit, and it only dropped .1 volts, according to the chart, that's only 1 ohm. That drop was most likely from the 8 feet of jumper I had going from under the vehicle to the battery.
After testing that ground, I felt fairly confident that it is a good circuit, but having never used it before, there was slight doubt in my mind.
Just now, a vehicle came in with one tail light out, and the customer had already changed the bulb, and the socket. After testing with my power probe, and seeing 11.4 volts on that circuit, I grabbed my new load tester, and multimeter, and saw the same reading, until I loaded the circuit. It immediately dropped to zero volts. I had the ground lead clipped to an aluminum rail on the bed of the truck, so I grabbed a t-pin, and probed the ground circuit at the connector, and retested. Same results. Took less than 5 minutes to determine that the tail light circuit was bad on that side.
After using this tool twice, and seeing two different results, I am happy with the purchase, and look forward to using it more in the future.