How to diagnose a bad coil?

[Jim Kroeger]

Is there a way to tell if the coil is on its way out on my 30 Model A? I know you can check for 6v at each terminal with a meter but will this diagnose if it is bad? Can they slowly start to falter therefore fooling you into thinking it is something else that is the problem on a rough running engine or once they go they go and the engine won't run anymore? Any adivice?