Vintage AC Spark Plug Cam Dwell Indicator Tool with Case Automotive Tool Antique

Vintage AC Spark Plug Cam Dwell Indicator Tool with Case Automotive Tool Antique. I have no idea how this works, therefore I cannot test it. It does look like it’s in very good condition, and has been kept in the case. It does include instructions. The item “Vintage AC Spark Plug Cam Dwell Indicator Tool …