Test Meter or Light:  Almost any method of testing continuity will work, from a simple test light to a digital multimeter.  The best way is with an analog multimeter capable of accurately measuring resistances of less than one ohm.  But as I said, any other method will work.  Meter shown in the picture is not included with the timing fixture.

After you get used to using the timing fixture, you will find that it also is much easier and quicker than trying to do it with a feeler gauge.

Note that it is the time of the breaker points opening that is important, not the distance that they open.  Setting them to open .020" with a feeler gauge will get them close, but using the timing fixture gets them right on.  It also sets them to open 180 degrees apart, important for best idle.

Purpose:  As the magnets in the flywheel pass by the first and second legs of the coil's laminated core, a voltage and current is generated in the primary winding of the coil.  As the magnets proceed on to pass the second and third legs of the core, the voltage reverses in polarity.  At the correct time of that reversal, the breaker points must open.  That reversal is what causes a high voltage to be induced in the secondary winding of the coil, resulting in a spark at the plug.

Timing Fixtures