Timing Light Accuracy
My biggest problems with timing lights through the years has been those whose wiring harness plugs into the light and is detachable. Seems the plugs always get loose and then make poor contact. Then, that's when you start having trouble with loss of signal, weak signal, inaccurate or no flash.
Now, I will only buy timing lights that first, have the wiring harness made into the light and secondly do not have a dial back feature. The engine is the best dial back unit you have. Simply use it for that feature.
Believe it or not, I found a vintage tuneup kit at a yard sale a while back. It has timing light, dwell meter, vacuum gauge, compression tester and a hand held remote starter switch. Made by Dixco. Remember them? The light thus far has worked well. It seems to be accurate based on the vehicles performance I have used it on.