I have found this specialty tool to be a very handy part of my automotive parts & tools. Sometimes when a motor vehicle fails to start its quite the mystery as to the cause. This is one of those tools that helps analyze this situation. What it does is checks for any spark when your auto fails to start for you. I used this once on a very old car. My friends and I could not figure out what was going on and someone suggested we check for a spark. There was none so we pulled out the distributer and rebuilt it with some new parts and carefully put it back in the car. It was a huge job but the car worked perfectly after that ordeal. I also used it on a more recent car that was always giving me problems. On that particular car there was a spark and the problem ended up being the starter. This specialty tool carries a lifetime warranty from AmPro. I would recommend this item for anyone who works on cars as there are many reasons why a vehicle does not start. Being able to determine whether or not a spark exists is pretty important. Parts are expensive and you do not want to be throwing parts at a car as in a guess whats wrong scenario etc. A nice tool for the automotive detective.