Hi Bob,
I'm not at all sure about the equation you posted.
Here is a picture of the one i have always used.
Its a picture because i dont know how to put those symbols in a post.
Hi Mike,
You would have seen ringing on an oscilloscope,
which of course is from the cap and coil primary,
but i think this is just an incidental effect and not part of the ignition system.
I think the cap is there just as a snubber, as Ron describes.
Ive never met an ignition cap as large as 3 mfd,
i seem to remember them as mostly around 0.047 mfd although i could be wrong,
it was a while ago, and i only mean 12v car engines.
Very little knowledge of 2 stroke or magneto ignition systems,
which may be quite different.
I once made a capacitor discharge ignition system, driven by the points,
it did give better performance, and virtually no wear on the points,
and smoother running through the rev range.
Most noticeably nice and smooth at low revs,
i was able to get the engine to run smoothly at about 450 rpm.
The unit failed some years ago, i still have the car, its back on normal points ingnition now.
(tickover has to be up around 550 to 600 now.)
John