My Dad had one of those in his services station. They work really well for setting advance curves as well as point’s gap and dwell. On the one he had (same brand)you could check voltage out-put as well.
You may want to check out EBay to see if some has a manual for it.
There is a place out here (California) that sell old service manuals, can’t think of the name right now. When I do I will pass it along to you.
