Its for setting the ignition timing.
It produces a loud beep noise, which changes when the breaker opens.
You put one wire on the case and one on the screw for the condenser cable on the breaker.
Set the distance beforce TDC with the gauge and then set the timing until it changes the noise.
I will make a video of this on tuesday, this tool works fine after 40 years of excessive usage.
if i see this right #8 shoudl be screwed in to the spark plug thread and press the gauge in it.
you need to test which extension (#5-#7) you have to use on the gauge.
Basicly #3 to #13 are iginition setting parts.