coil without ballst resistor?

Not having a scope and working with electronics, is like wanting to whittle without a knife. It is hard to fix, improve, or understand something you can't measure or see.

Calculations. Ohms law goes a long way. V= I x R. The method of using a resistor as a shunt to measure current is common. Current probes for for scopes cost hundreds of dollars.

By viewing coil current, not only is peak coil current measured, but how long it holds before released for ignition event. The peak current relates directly to potential spark energy. Time at current squared times coil resistance relates to coil heating. While measuring current with a meter gives a number, and is useful, it does not reveal details. Having detail, gives insite of ignition energy, and undesirable coil heating due to extended time at current.

There is much misunderstanding about dwell time. Dwell in points era is in degrees, of charge, and is limited by distributor cam. At high RPM, dual points were one makes, the other breaks gets provides ability to extend dwell. That gets job done with help of ballast to limit current, however very inefficient. The time it take to charge a coil is based on two things, voltage supply and coil primary inductance. For most coils it is a few milliseconds, it has almost nothing related to degrees. With degrees in control, charge time varies with RPM, at low RPM, charge time is hundreds of milliseconds, way longer than necessary. At high RPM on single coil systems the available charge time becomes a limitation. Spark is curtailed during charge, and energy in coil at that time is added, so it takes less time to reach peak. That saves the day, for achieving high peak spark energy, with reduction of spark duration. Spark duration is can run for a few milliseconds, based on coil discharge, and can exceed combustion event. Cutting duration, insures energy, yet sufficient for combustion. Just examples of viewing coil events as a waveform, showing time and magnitudes can be important. I hope many are curious is what their coil current looks like. I am preoccupied with home remodel. I hope to find time to post a how to on using low cost scope for automotive applications.