[mr0077]

KK has it right...the coil discharges (generates a spark) when the points open, causing the magnetic field around it to collapse. It will discharge in a very short time, but it takes time (at 12V) to charge, so the idea is that both points must be open at the same time to open the circuit and allow the field to collapse. The first set opens while the second is still closed...then the second set also opens, the field collapses, the spark occurs, and almost immediately the first set of points closes and allows the coil to begin to saturate (charge). As RPM increases, the saturation time (time the points are closed) gets shorter. A dual-point distributor will give a longer saturation time in a conventional ignition system, thus will provide good/stronger spark at higher RPM than a single point set. That's all moot if the points only switch an electronic box like MSD or Jacobs...then the charging is controlled by the electronics...