I just updated one of my 440's to an electronic ignition. I had never previously had a timing light on it as it ran great from the moment I purchased the car. Put in the new distributor and couldnt get it to run right without putting an excessive amount of timing in it. After checking to make sure the balancer hadn't spun, I looked at the timing tab. I had a couple other big block covers around, so I laid one on the bench with the TDC mark at 6 oclock, put a piece of masking tape around the balancer and marked TDC on the balancer and the 0 degree mark on the tab. I did the same thing with the engine in the car I was working on. I removed both pieces of masking tape, laid them flat, and the distance between the marks was over 1 1/2" from one to the other. It equated to a 22 degree difference so I ended up having to put a dial back light on it. Total timing reads 57 degrees, but in actuality is 35 degrees when accounting for the 22 degree difference. At first glance the tabs looked to be in the same place, but clearly they weren't. It took me awhile to figure out what was going on, but as someone else previously mentioned the timing tab could be mis located and not be overly obvious at first glance.