I have never used that tool so I'm not sure what or how you are reading. In general the voltage put out by the coil is whatever is required to bridge the highest form of resistance. An open plug wire (open means infinite resistance) will take the coil to its maximum output which is usually around 30kv (30,000v). The highest form of resistance is usually the plug gap under load. A plug setting on the motor outside the cylinder, will fire at probably a couple thousand volts, whereas the same plug firing in the cylinder under compression will fire at 10kv approximately.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician