Cable testers typically have a wrench that you put on one end of the cable and insert the other end into the device. You press the test button and the device tells you if the cable is good or not. I have several of these, of varying complexity and price range, but they are all similar in function. This device is not like that. It also has LED indicators on the button. When checked, the indicators light up both on the box and on the key. There is no indication of correctness, you need to watch the indicators on both the device and the key and make sure that the pattern is the same. For example, the correct wire will flash 1-2-3-4-5-6-7-8 in sequence on both the device and the key, and if the brown pair is reversed, the device will flash 1-2-3 -4 -5- 6-7-8, but the key would be 1-2-3-4-5-6-8-7. If you're just crimping a short wire, that's fine. If you run a cable over a long distance, you have to be in two places at once to observe the behavior. Or at least constantly running back and forth between two places, which is very cumbersome.