This is the three-wire spark inspection machine of gasoline engine ignition systems.
The failure can be diagnosed easily without removing the magnet equipment from engine.
Main body weight
When wired as shown in the installation diagram and the knob is set at 6 mm, if the engine starts, the ignition coil is good. This allows diagnosis in just a few minutes.
While the engine is running, the voltage generated by the ignition coil is indicated by the spark gap distance dialed in with the knob.