The spark plug in the engine translates electrical power to chemical action.  The electrical voltage is initially zero across the spark plug gap.  With an air/fuel charge in the gap, the charge is in the insulation state, and the spark voltage is zero.  Then, the first power action is the voltage from the distributor to charge the gap to reach breakdown voltage which changes the insulated air/fuel charge to a conductor, and ionized state.  The ionizing voltage is continuous through the timing of the burning interval.  The breakdown voltage that is viewed on an engine analyzer is a high sharp spike.  Whearas the ionizing voltage is viewed as a cyclic lower continuous voltage.  A misfire would exhibit no breakdown voltage, and no iozing cyclic voltage.