1st let me say I never had or heard a timing light read wrong before, as far as I knew. I've got a VW bug I just bought and trying to get it to run first thing is tuneup. Checked timing and it is about 170* off. I think it can't be because it is running. I start checking everything and finally think the timing light has to be wrong. I decided to borrow one but now not many folks have them, couldn't find one to borrow. Then decided to find another car to use the light on, again not a lot of people have cars you can time. Only thing left is to buy a new timing light, got it home and tried it and it worked perfect. I am glad it was so far off it was obvious something was wrong. If it had been just a few degrees off I would have never known and wondered why my car wasn't performing as it should or worse yet damage it.