You want to force your ignition to produce it's maximum output voltage.---It does not take " maximum output " to show spark on a plug grounded to the block.------And there is a difference in voltage requirement when sparkplug is in the cylinder with air compressed at 125 PSI.----Therefor you test as above.-----I have tested like that for many , many years.-----On more than one occasion folks have said---" I have never seen spark testing like that.--Did you make that tool ? "
